Other AUs
WIP
Reimarco College AU
Berumaru, Reijean, past Reimarco, unrequited Jeanmarco
Jock Reiner and nerd Marco make an odd couple but are very happy together... until Reiner realizes Bert has feelings for his boyfriend and that they might be returned. Reiner wants them to be happy, so he breaks up with Marco. It takes them a while of being just friends with benefits, but Berumaru do end up together, and Reiner and Jean end up getting closer because of their shared feelings for Marco.
FTM Marco AU
Reibert, Berumaru, Jeanmarco, eventual Berumarujean and past Reibert
Reiner notices how much Bert loves pussy despite being gay, so he recruits his FTM friend Marco for a threesome. Reiner ends up sidelined and their relationship never fully recovers. Bert keeps seeing Marco behind Reiner's back and Reiner has enough and kicks him out. Marco had been seeing Jean, who liked Marco enough to try a relationship with him and Bert, and the three end up happy together while Reiner is alone and miserable.
AU 1: Reiberumarujean
The threesome actually goes well because Reiner asserts himself instead of sulking off. They both realize they feel more for Marco and begin an open relationship, which Jean eventually joins via Marco.
Reiberumarujean Modern AU
Reiberumarujean though the Jean is mostly confined to Jeanmarco
Reiner, Bert, and Marco have been together for years and tentatively keep their relationship open despite having no real plans to ever sleep around with others... until Marco meets Jean and things Escalate. Jean still doesn't feel comfortable initiating with Reiner or Bert, but hey, things'll change.
MTF Bert
Reibert, Berumaru, Jeanmarco
Reiner and Bert were two married gay men before Bert realized she was a woman. Reiner said he would support her through her transition, and he did for a few years, but ended up unattracted to her and divorced her so she could find someone who truly loved her. This fucked her up and she was never the same person she used to be. After trying to date and having a miserable (and violent) time of it, she met Marco, who was with Jean at the time, and started a sexual relationship with him. But Jean felt they were getting too emotionally close and threatened Bert to back off. Bert tried to get validation from Marco, but he, to her mind, confirmed to her that he'd always choose Jean, so in her distress she killed herself. Reiner and Marco end up befriending each other after meeting while cleaning out her apartment because Reiner was still the only person in her will.