Echo does not often interact with Alice, however, the two seem to have an awkward and uncomfortable relationship with one-another, as shown when they were left with one another during the festival in Reveil that followed Oz's second Coming of Age Ceremony. It was during this time when Alice and Echo refused to talk with one-another, Alice only speaking with Echo to inform her that she had no intention of sharing her food with Echo. Echo would later confront Alice (only doing so because Vincent had ordered her to preoccupy Alice), displaying her true dissatisfaction of Alice because of Alice's constant worrying about Oz, as well as Alice's inability to remember Echo's name. The two proceeded to fight after Echo displayed her true colors, with Alice vowing not to stop until she landed a decent kick on Echo, showing in further detail the strained relationship between the two. However, despite Echo's apparent dislike for Alice, Echo saved Alice from being reduced to sand by Oz's power when Jack attacked her. Echo had claimed that this was an act that her body chose to carry out on it's own, however the reasoning for this remains unknown, leaving it possible that Echo's dislike for Alice is only what's on the surface of her opinion of Alice.
Echo had initially appeared to have been on good terms with Gilbert, the two sharing visible concern for one-another during their battles against Grim and the hoards of Humpty Dumpties at Yura's Feast. However, Echo's concern for Gilbert seems to be drawn from the fact that Gilbert is the elder brother of her master, with Echo knowing that she'd be scolded severely if anything happened to Gilbert on her watch. In reality, Echo revealed to Alice during a festival in Reveil that she finds Gilbert annoying because of his constant talk about Oz, however her feelings have yet to be elaborated beyond that point. Alternatively, Gilbert appears to view Echo with respect, but does not seem to give much thought to her, apart from the fact that she is his younger brother's loyal valet.
As Echo fights against Noise, just as she's about to give up, Oz's voice calls out to her, calling her name. When Oz appears, encouraging her on, Echo reminiscences about the times Oz called out her name and how he made her happy for some odd reason. Even when Echo felt that these feelings for Oz were strange, she was filled with happiness whenever he called her name and destroyed herself in order to protect Noise. As she lay on the ground, crumbling to stone, Oz knelt close to her, telling her he would call out her name no matter how many times, calling her "Echo-chan". Echo, with a small blush across her cheeks, quietly corrects him saying: "It's just Echo", before she ultimately vanishes.
Although Echo is loyal to Vincent, Echo has voiced her extreme dissatisfaction towards him as a person. Echo notably complained about Vincent's day-to-day habits, that lead the Nightray valets to avoid his room because of its insanitary condition, as well as Vincent's tendency to break his dolls and get angry when Echo attempts to clean them up, Vincent's tendency to fall asleep in random places - forcing Echo to deal with him, and finally how Vincent always wants Echo to sit on his lap when they sit together. Even though Echo has her complaints, she remains loyal to Vincent wholeheartedly, following his orders to the tee. Then again, Echo has also voiced her individuality against Vincent, as shown when she told Gilbert and Elliot about Break fighting Fang and Lily at the second Coming of Age Ceremony - despite Vincent doing all in his power to avoid such a revelation. Vincent has also shown that he uses Echo as a sort of punching bag, having taken out his anger after his encounter with Gilbert on St. Bridget's Day on Echo - often times coming up with excuses to justify his actions when someone else questions them. Still, Echo remains with the Nightray Dukedom, apparently requiring Vincent's approval to function - as shown when Echo was brought to tears because Vincent chose Noise over her. All-in-all, Echo believes that nothing is more important than loyalty.
Echo has an antagonistic relationship with her sister personality, Noise often times taking any opportunity she's presented with to talk down to Echo and do things that will hurt Echo emotionally, as she did when she fatally wounded Oscar in front of Oz. Noise also makes it her one of her prime goals to taunt Echo, and make her weak enough that Noise can force her way into being the dominate personality. Echo has also been shown to have a crippling fear of Noise - which she showcased by running away from Noise when Noise confronted her during the St. Bridget's Day festival. This being said, Echo is ultimately unable to do anything more than cry and accept her emotional pain that Noise inflicts, acting more out of fear than mustering up the courage to stand up for herself against Noise.
Despite this she is concerned about Noise as she is over taken by Duldee.