Lacie was born approximately 131 years ago as the younger sister of Oswald. As Oswald was born with a large distortion of Abyssal energy around his soul, it generated the creation of an aberration outside of the Abyss' power, thus making Lacie a Child of Ill Omen. Due to being a Child of Ill Omen, Lacie's existence attracted misfortune-- causing unspecified hardship toward both her and her brother during their early lifetime. At an unspecified point, Lacie and Oswald were approached by the Droplets of Light, which enveloped their bodies. From that moment on, the Droplets of Light guided them to Sablier and the Baskerville Clan, where they're taken in as valets of the acting Glen Baskerville at that time, Levi; being the destructive aberration of the Abyss and Levi's successor respectively. As such, Lacie was confined to "Lacie's Tower" in the forest surrounding the estate, rather than being free to live in the main estate like the rest of the Baskervilles.Shortly after their induction to the Baskerville Clan, Lacie was brought by Levi into the basement levels of the Baskerville estate to play with Oswald playing. All was well until Lacie ran into Jury, who asked why a Child of Ill Omen was in the estate, and ordered Lacie to "fall" immediately. Oswald called Lacie to him and away from Jury, while Levi approached her and told her not to scare Oswald and Lacie as they were new to the Baskerville Dukedom. Jury asked if Oswald was to become Levi's successor, which Levi confirmed, stating that he'd been making preparations for the first Succession Ceremony in order to transfer Raven to Oswald. However, Levi added that transferring all of the Black Winged Chains could take anywhere between 10 and 20 years, and so Jury would just have to bear with Lacie's existence until then.
When Levi returned, Lacie asked who Jury was, and so he explained that the woman was a Baskerville who had a different purpose than the rest of the Baskerville Clan, as Jury was to protect each Glen. Oswald asked why Levi needed to be protected, and Levi just said that it was the way things were; revealing that no one actually knew how long Jury had been around or where she stayed, all that was known about Jury was that she was the adviser to Glen who appeared in unexpected places at unexpected times and that it was best if they didn't ask why she existed if she already did. Instead, Levi made a point of how Lacie should've either been asking herself what she was going to do about Jury, or just accept her all together. With this in mind, Lacie wondered why Jury ordered her to fall back to where she came from; which Levi claimed was simply because Lacie was a Child of Ill Omen. Lacie didn't understand what that meant, something which Levi had expected, and so Levi elaborates that her imminent "fall" meant that she was going to die.
Later, once alone, Lacie was confronted by Levi, who explained that after Oswald took over as Glen he'd cast her into the Abyss. Lacie was confused by this, as she believed that she'd just come back as she always did. Levi tried to help Lacie understand that when Baskervilles spoke of casting someone into the Abyss, rather than sending them to the parts of the Abyss that were bathed in golden light, the Chains of Condemnation would be summoned to drag the individual into the heart of the Abyss, where their existence would be annihilated by the darkness within and the Rule of 100 Cycles wouldn't apply. Understanding that this meant she'd be dead for good, Lacie asked if she was going to be cast into the Abyss because she was a Child of Ill Omen; which Levi cheerfully confirmed.Sometime after learning about the heart of the Abyss, Lacie examined it from a far while visiting the Abyss. Lacie could sense a lonely female presence within the darkness, though she couldn't see who they were and they wouldn't answer her calls. Upon her return from the Abyss, Lacie asked Levi if there was someone inside the heart of the Abyss, though Levi wouldn't answer Lacie immediately, instead taking some time to think over the situation. Afterwards, Levi asked to meet Lacie alone again, asking if she remembered asking him about the presence in the heart of the Abyss. Levi explained that what Lacie likely felt was The Core of the Abyss, as Children of Ill Omen could connect to The Core; even though Glen Baskerville is the only person permitted to do so. For this reason, Lacie had to be cast into the Abyss, since The Core acted as the macrocosm of the Abyss and to touch her would result in major disruptions of the 1st Dimension. Such disruptions were why the Glens were the only ones allowed to approach The Core, and only in the most dire of circumstances, leading Levi to ask if Lacie finally understood why her existence was such a threat.
Rather than answering Levi's question, Lacie told him that she'd heard that the Chains of Condemnation could only be summoned by the Black Winged Chains; wondering if it was right to assume that her brother would be the one to kill her when the time finally came. Mulling over everything he'd told Lacie, Levi admitted that he really shouldn't have told her anything; but asked her if, since she was going to die anyway, she'd like to help him with an "experiment" of his.
Confused, Lacie asked what Levi meant by an experiment, with Levi revealing that he'd like to start an experiment to see if a human could control the powers of the Abyss. Writing it off as impossible, Lacie reiterated an old conversation between herself and Levi; where he claimed that the Abyss was something like a blueprint of the world, nearly god-like. Knowing what Lacie was getting at, Levi elaborated that he wasn't seeking to make a human a god, but rather to provide The Core with a human vessel through which they could potentially control the power of the Abyss. Stopping dead in her tracks, Lacie turned to Levi, shocked that he'd even propose such a thing. Seeing that Lacie thought his idea was outrageous, Levi stated that even though Lacie's body would be bound by the Chains of Condemnation when she was cast into the Abyss, a child within her womb wouldn't be condemned for the same sin; thereby allowing a child of Lacie's to be cradled in the darkness of the Abyss. Levi put his hand on Lacie's shoulder to console her, but she shook him off immediately, reluctantly asking if The Core would find said child and take it as her own vessel. When Levi confirmed this, Lacie agreed to take part in his experiment, not wanting The Core to feel so lonely anymore.
Sometime after her conversation with Levi, Lacie decided to venture back into the Abyss with twin black rabbit dolls; only this time she ventured into the heart of the Abyss. Lacie kindly greeted The Core upon their first meeting, giving it one of the rabbits so that it wouldn't have to feel so lonely anymore. As The Core played with the rabbit doll, Lacie asked if it liked the doll; promising to bring "another friend" with her the next time they met, that way The Core wouldn't be lonely when she was gone. At that moment, new life grew in the dolls; one soul shared between two bodies, and so when Lacie returned to the 1st Dimension, The Core remained connected to her through the doll.
At an unknown point, Lacie formed an Illegal Contract with Lacie's Chain.  Oswald also composed a unique melody, liking her brother's creation, Lacie added her own lyrics to the song and sung it often. Over the years, Lacie's love for the world took her to develop a routine where she'd stray from the Baskerville estate and dote on a random citizen of Sablier until she was forced to return by her colleagues, Oswald or Levi.A little more than 10 years later, Oswald had let Lacie win a game of chess against him, as he always beat her. This outraged Lacie, prompting her to change into a summer dress and run away from the Baskerville estate, hoping that Oswald would feel guilty knowing that she could freeze to death dressed like that in the middle of winter. Refusing to return until Oswald apologized to her, Lacie roamed around Sablier until she came across a young beggar wrapped in a blanket in an alley. Lacie introduced herself and asked what the beggar's name was; introducing himself as Jack, Lacie decided that Jack's name was too plain, which confused Jack, then explaining her situation to Jack. Jack, still confused about Lacie's actions, wasn't paying attention as Lacie carried on about her life, and when Lacie asked him if he was, Jack simply said that he didn't care about whatever she was talking about. 
Lacie asked Jack why he was talking so morosely when there's probably a lot of questions that he could be asking her. Though she attempted to start a conversation with Jack, no progress was made until Lacie joined him in his blanket in the alley. Jack ordered Lacie to get out, asking Lacie what she thought she was doing; which made Lacie excited because it seemed as though Jack had finally taken an interest in her. Finding himself lost in Lacie's red eyes, Jack was speechless; prompting Lacie to explain how her eyes supposedly meant that she was the cause of misfortune. Continuing, Lacie couldn't help but wonder if Jack was a little scared by her because she was a Child of Ill Omen, though she found that Jack wasn't paying attention; having lost consciousness from hunger.
When Jack woke, Lacie had returned with some stolen food. When the two ate together, Lacie elaborated, and revealed that she had told the shop keeper about their situation, hoping that he'd take pity on them and give them food, but when he didn't Lacie stole some food, a scarf, a spoon, clothes and a pair of scissors. Lacie had proceeded with cutting Jack's hair when she asked if he was related to the Vessalius Family in some way. Jack was shocked by this and asked how Lacie could've known that; with Lacie explaining that Jack had a golden token around his wrist bearing the Vessalius Family Crest. Jack told Lacie that the token was a memento from his mother, explaining how he was a the child of a mistress of Viscount Vessalius' and that his mother had been driven insane after Viscount Vessalius never came back as he'd promised. Lacie asked Jack if he hated his father for what he did, which Jack confirmed, also stating that he hated his mother and everyone else around him, though now he'd become indifferent and realized that he really never had anything in the first place. Upset with Jack for saying such things, Lacie stabbed Jack in the ear with the scissors; telling Jack that he was cute when his face is all scrunched up in pain. Adoring Jack for his embarrassment, Lacie said that Jack's claim of having nothing was a lie, leading Jack out of the alley and into the open streets of Sablier in order to show him her view of the world.
At some point, Lacie and Jack ventured outside of the town. While Jack was staring out into the distance, Lacie told Jack what she felt about the world. Lacie informed Jack that she viewed the world from every possible angle regardless how cruel and ridiculous the world have become. Despite this realization, Lacie informed Jack that even if he found what she had just told him hard to believe in, nonetheless she believed that this world is really beautiful. As Lacie grabbed Jack's arm, she secretly informed him her desire to have the chance of letting him see "that world" (the Abyss as the golden paradise) as well. Lacie pointed Jack to the sky and this caught Jack's attention; he was captivated by the sight of the stars in the night sky.
In an attempt to change Jack's view of the world, Lacie told Jack that resigning himself strictly to existence wasn't enough. Lacie implored that if Jack was hungry then he should eat, if he lacked money then he should have steal, Lacie even told Jack that with his attractive features he could sell his body if need be; though Jack wrote prostitution off as a dirty job, surprised that Lacie would even suggest it. Overtime however, Jack learned how to smile again as Lacie sang a song that Oswald had composed, open Jack's eyes to how important Lacie really was to him.Unbeknownst to Lacie, she'd caught the eye of two child traffickers while in Sablier, who stalked her and Jack until they wandered outside of Sablier. The traffickers then jumped Lacie and Jack, knowing how valuable a Child of Ill Omen can be to wealthy people that like to take them in as their pets. When Jack was injured by one of the traffickers for struggling to break free and help Lacie, who had been thrown to the ground after calling the trafficker that was holding her up off the ground a pig, Lacie finally snapped. Lacie summoned her Chain and the bladed chains it wielded, massacring the traffickers for hurting Jack and dancing in their blood as it rained down.
The Baskervilles appeared almost immediately to retrieve Lacie since she was never allowed to leave the estate without Levi's permission; having followed the power of her Chain to her location. Another Baskerville extended an apology from Oswald to Lacie so she would return home; making Lacie happy once again as she turned to Jack and told him that it was time for them to part ways. Jack explained that if they're ever meant to meet again, they will, which pleased Lacie and prompted her to give Jack one of her earrings as a memento. As Lacie left, Jack said that they will meet again because he will never forget the Baskerville name. Eight years go by, and during this time Oswald successfully underwent Succession Ceremonies for Raven, Owl, Dodo and Gryphon, bringing him closer and closer to his destined position as Glen Baskerville. Lacie and Levi on the other hand begin Levi's experiment, Levi impregnating Lacie nine months before she's meant to be cast into the Abyss. Five months into her pregnancy, Lacie laid on the floor in her tower, reminiscing about the golden light of the Abyss. Levi burst in and informed Lacie that he couldn't live up to his promise to take her off the estate that day, as he'd forgotten about the event he'd organized in Arthur Barma's honour. Noting that Levi had so far broken nine of his promises, Levi smiled and replied that after one more they'd be able to celebrate the anniversary of their tenth broken promise. Lacie made sure to mention how after the Barma Dukedom lost the power struggle in their homeland and were exiled they'd been trying desperately to get in favor with the Baskervilles. Levi argued that it was good to experience foreign cultures, inviting Lacie to the event if she wished to attend; leaving Lacie to consider his invitation as he proceeded back to the estate.
Ultimately, Lacie decided to accept Levi's invitation, though when she arrived she was instantly embraced by the musician who'd been playing a morin khuur from the Barma's homeland. Lacie was shocked and unsure of what action to take as the man rejoiced over how he'd finally found her after eight long years. Levi made sure that Oswald hadn't killed the man so that he could interrogate him, and Oswald asked if Lacie knew him. It wasn't until then that Lacie noticed that the man was wearing an earring, prompting familiarity in Lacie; though she still denied knowing who the man was. While Levi and Oswald dealt with the man, Lacie ran to her tower to try and decode the nostalgia she was feeling. Eventually, Lacie remembers something, rifling through her jewelry box and finding a sole earring that matched the man's; reminding her of how she'd given the other to Jack.
Lacie wastes no time and returns to the mansion to save Jack from his interrogation; only she arrives just as Jack throws water on Oswald for embarrassing him. Lacie subtly steps in and drags Jack out of the mansion, leaving Levi in a fit of hysterical laughter over the awkwardness of the situation. As it started to snow, Lacie questioned if Jack is calmed down, though Jack continuously stumbled over his words, making Lacie glad to see that her lovable Jack hadn't changed at all since they met last. Brought to tears, Jack noted how he'd learned so much after losing Lacie, and that he'd devoted himself to reuniting with her in hope that she'd praise him for it. Lacie held Jack in her arms and guided him to his carriage, asking what he intended on doing now that he's satisfied his ultimate goal. Unsure, Jack debated whether or not he'd carry on living under the Vessalius Dukedom, though he was overjoyed about his reunion with Lacie. As Lacie went to speak, Levi came up from behind her, inviting Jack back to the Baskerville estate and providing him a map that indicated where to enter from. After jack left, Lacie asked what Levi planned on doing with Jack. Though he was unsure, Levi wrapped his arms around Lacie and admitted to having become rather fond of Jack in their short time together, asking if Lacie had done the same. Lacie slapped Levi's hands off of her and wrote off his assumption as preposterous since she was going to die soon anyway.
Over the course of the next four months, Jack continuously returned to the Baskerville estate to visit Lacie. On one occasion, Lacie, Jack and Oswald were sitting by the pond just outside of Lacie's Tower, when Lacie began singing. Recognizing the song from his first encounter with Lacie, Jack asked what the title of it was. Lacie denied knowing the song's name, as it wasn't her's, Oswald had composed it and she'd added the lyrics later on. Embarrassed, Oswald admitted that he'd never bothered giving the song a name. With this in mind, Jack proposed that they name the song "Lacie", surprising Oswald with his eagerness. Jack explained that during the eight years he'd spent searching for Lacie, whenever things looked bleak he would sing the melody to himself. Even though he didn't know the lyrics, the melody always made Jack feel as though Lacie was there by his side; which was why he thought "Lacie" would be a good name for the song. In his belief, the song that Lacie always sing embodied everything that she was. In the end, Oswald felt that naming the song wasn't overly important, giving Jack permission to name it if he so desired. Thrilled, Jack asked Lacie if she was all right with him naming the song "Lacie". Lacie simply replied that as long as Oswald was fine with it, Jack could do whatever he liked. Jack thanked Lacie for her approval as she walked away. Unknown to Jack, Lacie was blushing slightly as she was touched by Jack's suggestion to name the song after her. This was noticed by Oswald, who was surprised to see an expression on Lacie's face.
Afterwards, when Jack and Lacie were alone inside the mansion, Lacie crept up and sat on Jack's lap. Lacie held Jack close to her, ran her fingers his hair and looked into his eyes. Jack questioned Lacie's actions, though Lacie just announced that there was indeed something wrong with Jack; making Jack smile. In truth, Lacie had noticed that something wasn't right with Jack from his actions because they weren't within the natural human disposition; though when she looked into Jack's eyes she saw what she always does: nothing reflected back. Even so, Lacie's time spent with Jack was most pleasant as it eased her mind; though she never told Jack.
Five days before Oswald's final Succession Ceremony, Lacie was suddenly awoken after having a nightmare about the time she had met Jury. Levi, having arrived earlier, asked what it was Lacie had been dreaming about that made her shake so violently in her sleep. Ignoring Levi's question, Lacie instead noted how worn Levi seemed to be; something which Levi couldn't deny as his body was continuously growing weaker as it deteriorated. Encouraging Lacie to rejoice, Levi revealed that in five days Jabberwock would finally be transferred to Oswald during the final Succession Ceremony. This meant that Oswald would finally take on his position as Glen Baskerville, and Lacie would finally be cast into the Abyss.
Peering out Lacie's window, Levi sees Oswald guiding Jack to Lacie's tower; questioning why Oswald always went to meet Jack even though he was no good with Jack. Lacie corrected Levi, saying that Oswald had really started liking Jack. In fact, Lacie revealed that when Oswald said that Jack disgusts him upon their initial introduction, what he'd really been trying to say was that he couldn't explain Jack's nature and that it made him exceptionally curious about him; however Jack had once admitted to Lacie that he found Oswald rather frightening because of how they made him feel like he was being interrogated with every stare. Confidently, Lacie stated that she felt as though both Oswald and Jack were great friends, prompting Levi to voice his surprise over how well liked Jack seemed to be. Lacie agreed, noting how it wasn't common for Oswald, though as Levi came within inches of Lacie's face he revealed that he was talking about her; having initially believed that Lacie was just leading Jack along, Levi could now see that even Lacie had been charmed by the lost puppy who'd yearned for her affection for eight years. Unexpectedly, Lacie denied her feelings toward Jack and instead claimed that such assumptions bothered her because she was just playing with him to waste time before being cast into the Abyss.
Proceeding outside with Oswald and Jack, Lacie told Jack of the Succession Ceremony and how Oswald would officially succeed Levi as Glen Baskerville. In addition, Lacie noted how busy the Baskervilles would be preparing for the Succession Ceremony and asked Jack not to visit until afterwards. Without knowing the true nature of what was to come, Jack agreed and asked Lacie when the event was going to take place. Smiling, Lacie lied and told Jack that Succession Ceremony was scheduled for a week from then, bidding Jack her final farewell as he left the Baskerville estate.
Oswald escorted Lacie back into her tower, asking her why she lied to Jack. Lacie explained that there wasn't really a point to telling Jack the truth, wondering if Jack would've broken her out of the Baskerville estate in order to save her had she told him the truth. Solemnly, Oswald mentioned how if that was what Lacie wanted, Jack would've done it for her; prompting Lacie to hug her brother and apologize for being so harsh. Assuming that Oswald didn't feel guilty for what was going to happen to her, Lacie explained that even though her eyes brought them a great amount of suffering over the years, she never once felt sorry for herself or depressed because her eyes allowed her to see the true cruelty of humans; which allowed her to see their true beauty as well. Furthermore, Lacie stated that it was all about looking at the world from different angles and allowing yourself to see how wonderful things could be, which was why she loved their world. Oswald found himself at a loss for words, marveling at how strong Lacie was and admitting that he'd be lonely when she died; catching Lacie off-guard. Later that night, Lacie wandered the grounds of the estate, thinking of how Oswald said he'd be lonely without her. Leaning against an old tree, Lacie finally understood that the darkness in her heart that she'd been trying to hold at bay was her own loneliness. Lacie watched the night sky, knowing that it wasn't like her to feel that way, ultimately blaming Jack for making her realize her anxiety over disappearing from the world and not being able to be with him anymore too late.Before Oswald's final Succession Ceremony, Lacie returned to the heart of the Abyss with her black rabbit doll, apologizing to The Core for it being so long since they'd last met. Lacie told The Core that this would be her last visit because she was going to be cast into the Abyss, something which made The Core shudder with depression. Placing her black rabbit doll with The Core's own, Lacie expressed her optimism that The Core would befriend her child, before leaving the Abyss, never to see her old friend again.
Upon her arrival back in the 1st Dimension, Lacie attended Oswald's final Succession Ceremony, where she witnessed Levi summoning Jabberwock and draw his blood. As Oswald ingested Jabberwock's blood, Levi cut his own wrist and poured his blood into a chalice for Oswald to drink after Jabberwock's. Finally, Levi removed his cape and put it on Oswald, all the Baskervilles in attendance save for Levi and Lacie bowed before Oswald; recognizing him officially as their new Glen.
Soon after, Oswald, Levi and Lacie gathered to perform the portion of the Succession Ceremony involving Lacie's judgement. Lacie knelt before her brother, who put his hand on Lacie's forehead, announcing that he'd now pass judgement on Lacie with his Black Winged Chains. Oswald hesitated, not wanting to cast his sister into the Abyss as he was meant to, but Lacie asked him what was wrong and encouraged Oswald to get it done and over with. As per Lacie's request, Oswald continued, condemning Lacie for her sin of being born with the crimson eyes of ill omen, which threatened the harmony of the Abyss. using the power of the Black Winged Chains, Oswald opens The Path and draws forth the Chains of Condemnation, which wrapped around Lacie to drag her into the darkness of the Abyss. Before her descent however, Lacie made a point of telling Oswald something, shocking him as she left the 1st Dimension for the last time.
As Lacie was about to be cast into the Abyss, Lacie noticed something peculiar at her side. To her surprise, it was actually her brother but in his future successor's body instead. Oswald was shocked to discover Lacie was able to notice him when she called out to him. Lacie apologize to Oswald with a sad smile on her face. Her expression caused Oswald (his future self) to realized that Lacie was actually apologizing to his future self rather than himself from the past. It also caused Oswald to questioned as to why Lacie was apologizing to him, as if she have everything figure out at the time. Oswald asked Lacie, as he falling back into the time vortex, not to smile at him with that troubled look on her face.Returning to the heart of the Abyss in the embrace of the Chains of Condemnation, Lacie's body and soul immediately began to be torn apart by the darkness of the Abyss, however due to the distortion of time in the Abyss, Lacie went into labour at the same time and gave birth to twins named Alice; whose existences were stabilized and free from the grip of the Chains of Condemnation. Both twins' ages were immediately accelerated by a paradox while they were cradled by the smiling Core of the Abyss, who took one of the twins as her vessel, becoming the combined existence known as the Intention of the Abyss. The other Alice grabbed one of the black rabbit dolls, now belonging to The Core, and left the Abyss through one of the Doors to the Abyss. Upon the creation of the Intention, the harmony of the Abyss shattered and the golden paradise faded to darkness immediately, distorting the flows of time and transforming the Abyss into a primal state comparable to a hellish toy box. At the same time, the Intention intervened in Lacie's destruction and saved a piece of her mother's soul which contained her thoughts and feelings relating to Jack from being destroyed.
Jack returned to the Baskerville estate two days after the Succession Ceremony, only to learn from a depressed Oswald that Lacie was dead and that he'd killed her. Oswald made sure to give Jack Lacie's matching earring to the one she'd given him eight years before, allowing Jack to leave and return to the Vessalius estate distraught. Alice escaped the Abyss mere days later, confirming to Levi that his experiment was a success, however Levi made sure to keep the nature of Alice's origins hidden from Oswald. It wasn't until a month after Lacie's demise that Levi ventured to the Vessalius estate to retrieve Jack, fully disclosing to him the secrets of the Baskervilles and the Chains that encircled their world. In addition, Levi brought Jack back to the Baskerville estate and showed him Alice, explaining her origins to Jack in order to allow him to carry on with the experiment, as Levi was on the verge of death.
Now alone, Jack made his way to the pond where he, Oswald and Lacie used to spend their days, meeting with Oswald; who was surprised to learn that Jack was still alive. Jack found how Oswald expected him to kill himself because of Lacie's death amusing, since he wouldn't die as long as he still had his hope, and if you lose your hope then despair couldn't exist either. In other words, Jack wanted to win back his hope, extending a hand to Oswald and suggesting that they go see Lacie together. Hearing this, Oswald slapped away Jack's hand and asked what he was talking about, as Lacie's existence had been destroyed and it was impossible to bring her back. Jack realized that Oswald had truly taken on the role of Glen and that if he pursued his intent to restore Lacie, then Oswald would cut off his ties with the Baskervilles. Apologizing, Jack suggested that they go see Alice, though Oswald denied Jack such luxury, wary of Jack's intent. As such, Jack decided to climb a tree beside Lacie's Tower and enter through a window instead. In the end, Jack fell, though Alice heard his fall and ran to the window to see what was going on.
Through her connection with Alice, the Intention heard Jack's voice and immediately recognized him from what she'd seen of Lacie's memories. The Intention ran to retrieve the piece of Lacie that she'd saved, giving it to her black rabbit doll (now named "Oz" by Alice) and asking him to take it into him body and deliver it to his body in the 1st Dimension so that Jack could see what the Intention believed Lacie wanted him to see. Loyal to Lacie, Oz did what the Intention asked of him, though the piece of Lacie he'd taken into his body was tainted with the darkness of the Abyss and it immediately began destroying his body in the 1st Dimension. Fortunately, this managed to grasp Jack's attention, and so when Jack picked up Oz, Oz delivered the last fragment of Lacie's existence to Jack so that he could see Lacie's thoughts and feelings about him. After experiencing this, Lacie's existence truly vanished from the world forever, but Jack unfortunately believed that Lacie had instead become one with the Abyss and was sending him a message; leading him down a dark path to reunite with her once more.