During an escape from the vampire city they were raised as livestock in, Yu was the only one to escape from a trap by Ferid Bathory that resulted in his orphanage family being killed, where he also had to leave Mika behind.Motivated to enact vengeance against vampires, four years later Yu becomes a member of the Japanese Imperial Demon Army, and joins Shinoa Hīragi's squad in the Moon Demon Company. Trained in part by Guren Ichinose.