The Keys to the Abyss are artifacts within Jun Mochizuki's Pandora Hearts. The Keys are concentrated forms of Abyssal energy that allow its users control of its respective Door to the Abyss. A Key to the Abyss in its true form appears simply as an orb of light, but it can be placed within any ordinary object for safekeeping. The Keys possess the ability to open and close the Doors to the Abyss, thereby restricting the flow of power from the Abyss into the 1st Dimension and other outside sources, such as Contracts. Due to the Keys not possessing a fixed shape, they can be difficult to obtain, especially when the Key itself will disappear if its owner is detained through violence. In addition to being able to unlock the Doors to the Abyss, the Keys are also capable of opening St. Luca's Gate, which Pandora used as an emergency exit when the lives of the Four Great Dukes were in potential danger, being located within the catacombs of Pandora.
The Baskerville Clan was in possession of all five Keys to the Abyss prior to the Tragedy of Sablier, having had control of all five of the Doors and their respective Black Winged Chains as well. Following the Tragedy of Sablier, Jack Vessalius instated the Four Great Dukedoms to become political super powers in order to cover up the true events of the Tragedy of Sablier. What solidified the Four Great Dukedoms' place above the rest of society was Jack's acquisition of four of the five Doors to the Abyss.
The Vessalius Dukedom would keep Gryphon's Door to the Abyss. The Nightray Dukedom - included in order to keep an eye on the Nightrays due to their previously close relationship with the Baskerville Clan - would receive Raven's Door; which was otherwise unusable due to Raven having formed a bond with Gilbert prior to the Tragedy of Sablier, thus preventing anyone else from forming a Contract with him. The Barma Dukedom - for their aid in the Tragedy of Sablier as Jack's accomplices - would receive Dodo's Door. Finally, the Rainsworth Dukedom - included in order to act as a third party that had been completely uninvolved in the Tragedy of Sablier - would receive Owl's Door.
With each Door, each of the Four Great Dukes also received a Key to the Abyss, which they secretly hid in personal items in order to keep them on their person at all times; a tradition which would go on across generations for more than 100 years.
Keys (Present Forms)
- Raven's Key: The Rapier - Sometime after becoming head of the Nightray Dukedom, Bernard Nightray put Raven's Key in his precious black-bladed rapier, as it is the very symbol of the Nightray Dukedom. True to his duty, Bernard kept the rapier by his side at all times - that is until Gilbert finally managed to form a Legal Contract with Raven. At this point, Bernard realized that his youngest son, Elliot Nightray, would never get the opportunity to try his hand at forming the Contract in order to represent the Nightray Dukedom honorably. As such, Bernard passed his rapier down to Elliot so that Elliot could represent the Nightrays in his own way - completely unaware that he was protecting Raven's Key while doing so. Sometime prior to Oz's second Coming of Age Ceremony, Vincent Nightray learned that the rapier held the Nightray Key. With this in mind, Vincent stole the rapier after Elliot succumbed to his wounds while denying Humpty Dumpty. Since then, Leo has been realized as the reincarnation of the soul of Glen Baskerville. While Oswald temporarily took control of Leo's body following Jack's second attempt at dropping the world into the Abyss - Oswald restricted the flow of power from the Abyss to all Nightray Contracts using Raven's Key, though this would prove to be futile as Gilbert would reform his Contract with Raven as a Baskerville instead. Following the eradication of Oswald's consciousness and the subsequent aversion of a second Tragedy due to the joint efforts of Oz and Leo, Leo would continue to keep Raven's Key in his possession as the Baskervilles retook their place as guardians of the powers of the Abyss.
- Owl's Key: The Locket - When Sheryl Rainsworth became Duchess, she hid the Rainsworth Key in a silver locket of her's. However, after Rufus presented Dodo's Key to her as a representation of a promise between the Barma and Rainsworth Dukedoms, Sheryl gave Rufus the locket in return - furthering their promise and making it impossible for them to betray one another. Many years later, after Rufus had reclaimed and destroyed Dodo's Key, he used used the Owl's Key to suppress the power flow to the Rainsworth Contracts in order to make it appear as though he'd destroyed the Owl's Key for the Baskervilles' own good as part of a ploy to gain the Baskervilles' trust. Rufus then sent the locket to Lutwidge Academy in a package with one of the Barma valets to ensure that Reim Lunettes would receive it. Afterwards, Reim used the Owl's Key to reinstate the flow of power to the Rainsworth Contracts so that Sheryl, Sharon Rainsworth and Xerxes Break could save reclaim Pandora from the Baskervilles and work to save the world alongside Oz, Alice, Gilbert and Reim. It can be assumed that in the events that followed, Owl's Key remained with Reim up until after the aversion of a second Tragedy. It is likely that Owl's Key was eventually returned to the Baskervilles sometime after.
- Dodo's Key: The Earrings - Prior to becoming the head of the Barma Dukedom, Rufus Barma received a pair of earrings from his mother, which contained a rare flower from The Barma Homeland. Ultimately, Rufus decided to hide the Barma Key in the earrings, which he soon presented to the woman he loved, Sheryl Rainsworth, in place of the roses she'd already declined. With this, Sheryl also gave Rufus Owl's Key to symbolize a bond between their Dukedoms to ensure that an event like the Tragedy of Sablier never happened again. Many years later, Rufus formulated a plan to dupe the Baskervilles after having learned the truth of the Tragedy. Rufus attacked Sheryl with Dodo in order to steal back Dodo's Key and gain the trust of the Baskervilles. As Sheryl was the only other person to know that the Key was actually Dodo's Key, everyone believed Rufus to be a traitor. In the end, Rufus destroyed Dodo's Key with the power of Dodo, thereby severing all Contracts under Dodo temporarily, while he suppressed the power flow to the Rainsworth Contracts in order to make it appear as though Owl's Key had been destroyed. Eventually, Dodo's Key would have reformed, thus reinstating the Barma Contracts. It is likely that Dodo's Key was eventually returned to the Baskerville Clan as they returned to their position as guardians of the power of the Abyss.
- Gryphon's Key: The Wedding Ring - Although Xai Vessalius, being the eldest brother, was meant to inherit the title of Duke, for reasons unknown Oscar Vessalius took the position instead. While Oscar lacked the ability to form a Contract with Gryphon as he was meant to, he could still hide Gryphon's Key, which he decided to put in Sara Vessalius' wedding ring in order to honor the memory of her. Oscar kept the wedding ring on a necklace that he wore at all times up until after the destruction of the final Sealing Stones. After this, Oscar used Gryphon's Key to open St. Luca's Gate in order to help Oz, Gilbert and Alice escape from the Baskervilles. During the escape attempt, Oscar was killed by Xai, who later then took Gryphon's Key for himself. As Xai was in possession of the Key at the time, it is unknown what became of Gryphon's Key following his death in Sablier when he protected Ada Vessalius from The Cook; however he may have given it to Oswald due to his loyalties lying with the Baskervilles.
- Jabberwock's Key: Unknown - As Jabberwock's Door to the Abyss was the epicenter for the Tragedy of Sablier, being where Jack had Oz sever the Chains of the World, Jabberwock's Door was lost to the deepest regions of The Hole when the majority of Sablier dropped into the Abyss; where the power of the Abyss often leaked out and mutated any who delved too deep. As anyone not considered a Baskerville was unable to approach Jabberwock's Door, Jabberwock's Key also remained inactive for more than 100 years. It wasn't until the reincarnated soul of Glen Baskerville, Leo, took on his responsibilities as Glen that he formed a Contract with Jabberwock, likely also obtaining Jabberwock's Key in the process; though what Leo put Jabberwock's Key into remains unknown.
- It's unknown what became of Gryphon's Key after Xai stole it from Oscar; be it whether he gave it to Oswald or kept it for himself until his demise.
- It is not known how long it takes a Key to reform - as Dodo's Key reformed sometime between the present events of Retrace CIV: Will and the epilogue.
- Despite Jabberwock's Key existing, it was never mentioned in Pandora Hearts.