Akuma Kirin

Currently a work-in-progress, but here's my (rough) ideas at the moment;

Joined DWMA; had to partner with Stein, despite him having already graduated, because none of the new meisters could resonate with Akuma. He burned the hands of anyone who tried. Supposedly the reason for this was Akuma's erratic soul (and his own inability to control it); it didn't have a consistent wavelength to be resonated with. Stein was the only one able to resonate with Akuma because of his incredible control over his own wavelength. Because of Stein’s skill, Akuma was able to become a Death Scythe rather quickly. Akuma gained more control over his wavelength after this; meaning it should be possible for Shinigami-sama to wield him if necessary (though likely for only a short period of time, before Akuma loses control).

Akuma’s issues with his father and overcompensating for his own anxiety and cowardice; are toned down after becoming a Death Scythe, something his father was not able to do. Though it's likely that Stein’s influence helped as well, surprisingly.

Akuma’s soul is not a healing soul, but it does require a level of focus to ‘tame’ it so it prevents Stein’s soul from becoming Madnes-inflicted by giving it something else to focus on. Stein is the only person this works on; everyone else ends up with some form of ‘soul illness’ (basically their own souls become erratic temporarily, making it difficult or even potentially impossible, for them to resonate with their usual weapon(s)) if they try to resonate with Akuma for too long (even after he’s become a Death Scythe).