Some art of my DMC OC Seraphime. I don't have a distinct backstory for him, outside that he was once a member of the Order of the Sword and "died" during experiments to combine man with demon under Agnus' care. His weapon, his Demon Arm, is "Anubis" and has a mind of it's own. Likely the tool that brought him back to life and balanced the chaos going inside his body.
Some ideas I had for his life before things went down is that he and his family were rescued by the Order when escaping Vie de Marli by boat a few years before the events of DMC2 About 2-3 years before the events of 4 he'd have volunteered as the first subject to test Agnus' treatment upon the recovery of the Yamato (some shards not withstanding).
Likely, after waking up and in a fugue state he'd have escaped Agnus' lab, while no one was there, with the aid of Anubis and taken to traveling until he could piece his mind back together. A natural redhead, it's hard to say what his original eye color was, but the blue is definitely a dye choice to give him a more distinct appearance. As is the side-shaved mullet-fohawk look.
Seraphime and Anubis are a team and work in-sync with each other, akin to how a Hexblade Warlock in D&D would work with their pact weapon~!