Mana Walker: Mana adopted Allen prior to the story. Mana treated Allen like a son though at times called Allen the name Allen despite the fact Allen didn't have a name at the time and the name Allen actually belonged to Mana's deceased dog hinting that along with his sanity slapping, Mana started to confuse Allen with the dog. When he was killed and revived as an Akuma, Allen was so shocked that his hair turned white and he synchronized with his innocence. He frequently thinks about Mana and his motto "Don't stop, keep moving forward". He even went as far as adopting Mana's personality, the polite speech of Mana being the most prominent trait. Recent revelations make Allen wonder if Mana really loved him or what is inside him.
Timcampy: Timcampy is Allen's (formerly Marian Cross's) loyal golem. The two care greatly for each other with Timcampy even refusing to leave Allen's side when he was dying as he did not want to leave Allen along with a Noah. When the two reunite the two break down in tears crying. Timcampy is loyal to Allen and in turn Allen deeply cares for Timcampy.
Marian Cross: Cross is the master of Allen, who takes guardianship of him after Mana's death. He wasn't the best guardian -abandoning Allen to find HQ on his own, 3 months prior to the story, teaching him how to gamble at a young age, and even having Allen pay his debts -though he does that to many, and Allen is just no exception, but got the brunt of it due to living with Cross for years. Allen has had a few bad things to say about his master earlier in the series, such as calling him a demon, and stupid master. Cross also refers to Allen as "Idiot apprentice" most of the time. However, the two do care for each other. According to Hoshino, Cross regards Allen as his own child, and thinks that Allen is cute. In turn, Allen was very distraught when he saw all the blood in Cross' room, believing him to be dead. When he faces the one responsible for attacking his master, he becomes enraged -further stating that he's Cross' apprentice and the thought of allying with the one who killed his master makes him sick. After meeting Cross again in Nea's inner world, he mentions that even if Cross is an illusion, he is happy to see him again.
The anime changed Cross' character, making him more of a villain, thus his relationship with Allen is changed with him being cruel or careless to Allen in ways that weren't shown in the manga. In episode 25, Allen mentioned that he never connected Generals with niceness due to his experience (with Cross). In episode 27, he mentions it again before telling Lenalee stories of how awful Cross has been to him. Things in the episode include Cross throwing Allen to legions of Akuma without training him. Forcing Allen to gamble and stealing his money -without need. Having Allen doing slave labor on loading docks, and hauling spice in deserts. Sending Allen into bouts of depression. And telling Allen to bring him man-eating animals -which almost gets him killed. In the manga, Allen only mentions gambling to make money -the slave labor hasn't been shown or mentioned. Allen also mentions that Cross lives off of lovers, and that he gambled if he and Cross were broke -contrary to the anime where he was forced to gamble whether Cross was living off of lovers, or not. In Hallow, there were cases of taking out lines from Cross that show his conflict over Allen. In the manga, during his hug with Allen, he wonders if you always have to sacrifice something to protect something else. He also notes that he can no longer make fun of Tiedoll (for being affectionate with his pupils). Meanwhile, in Hallow, Cross mentions how the fourteenth should have picked someone else, but took out his line about sacrifice and his realization with Tiedoll. There's also cases where Cross' facial expression are changed, and he's shown scowling at Allen in scenes he wasn't in the manga.
Kanda Yuu: Allen and Kanda frequently get into physical and verbal fights, Kanda calling Allen "Moyashi" (Beansprout) and the latter calling him "Bakanda" (Stupid Kanda). From their first encounter, Allen immediately found him associal and unpleasant though he usually is polite with everyone. Kanda on his side is cold to everyone but has particulary threatened Allen more than once. Allen described their relationship as "muscular". Even though they constantly fight, Allen deeply cares for Kanda, as shown with his worry in the Noah's Ark and his efforts to save both him and Alma Karma. Kanda confessed feeling remorse for stabbing Allen and letting the 14th awaken. Kanda is one of the very few people who can anger Allen, which is a peculiar fact since getting angry is reminiscent to Allen's former personality before his encounter with Mana.
Lenalee Lee: Lenalee and Allen treat each others very kindly and friendly as they have very similar personalities even if at times Lenalee already hit Allen. They genuinely care for each and consider each others like family. At first, Lenalee blamed him for getting himself in danger but Allen finally realized how much she cared for him. As a part of "her world", Lenalee can't stand losing Allen. When Allen was considered dead, she had a momentary depression. Allen and Lenalee several times dreamed of each others. When Allen left the Order, Lenalee chose to stay by his brothers and compagnons, she now blamed herself for it. Allen stated that even if he leaved, the Order with Lenalee and the others will allways be "home". Some scene may imply romantic feeling between both.
Lavi: At their first encounter, Lavi said that he could be a big brother to Allen and he seems to treat him like this. Due to Lavi's conflicted personality, it is hard to know which declarations and acts are genuine but it is safe to assume that at least at Edo arc, Lavi really cared for Allen and considered him as a younger brother as shown by his reaction to Tyki's provocations.. In a Talk Corner, Allen declared that he would have Lavi as the cool neighbourhood. Lavi is a very close friend to Allen and when the former had been mind controlled by Allen he couldn't bring him self to attack Lavi and chose to be killed rather than killing his friend. Allen and Lavi usually get along very well, Lavi being teasing and playful and Allen being easily entertained by Lavi's antics.