These are a number of relevant characters from Allen's time in Paradisa that had enough of an effect to warrant mention.

Teresa: A half-human, half-yoma (demon) warrior who was considered one of the best warriors of her world. She met Allen when he was about 16 and took him under her wing, over time becoming the closest Allen's ever had to a mother. Currently deceased.

Crowley: A demon that is actually pretty terrible at being a demon. They met in Paradisa when Allen was about 16, and over time Crowley became something of an uncle to Allen. Currently in the fleet.

Ino: A ninja from Konoha that Allen has known since he was 15. They have a fire forged friendship that has been brought on by years of being in Paradisa. Has a history of terrible boyfriends but is possibly the only person to out stubborn a shonen. Currently in Konoha.

Arthur: Allen's ex. We know he was involved in politics and he might possibly be someone of legend, but Allen's not too keen on sharing the details. It was a very bad break-up. Currently deceased.

Lenalee: Allen's other ex. She's an Exorcist from Allen's world. This break-up was much less terrible, and they remained friends afterwards. He'd appreciate it if you never tell Komui about dating his sister. Currently back in Allen's world.

House: The doctor that taught Allen the most about medicine after Allen bribed him with an interesting case. Was the one to discover Allen's Noah problem to be a genetic one. Currently without lupus.

Jr.: A hotheaded gunslinger from the future. He has a lot of secrets and issues, but Allen considered him to be one of his best friends. Currently traveling space elsewhere.

Guts: A large swordsmen that notably has worse luck than Allen. They were good friends, though Ino was much closer to Guts. Status currently unknown (alive).

Griffith: Someone from Guts's world that sacrificed his own comrades to become a demon. Wrought havoc in Paradisa so severe it earned a high spot on Allen's shitlist. Don't bring him up. Currently needs to die.

Riful: A gut-eating monster that killed and tortured many, including Allen and several of his loved ones. It took him over two years to defeat her. Don't bring her up. Status currently unknown (deceased).

Arthas: A lich king who killed so many in his world, he put a few races on the Endangered Species List. He worked as Riful's partner, also killing and torturing many in Paradisa. His sword contains so many trapped souls, Allen couldn't go near him without risking incredible pain. Don't bring him up. Currently deceased.