When Yūichirō (also known as Yū) was twelve years old, he and his best friend and fellow orphan Mikaela plotted a plan with other children from the Hyakuya Orphanage to escape the vampires' captivity. However, their plan was foiled kwa Ferid Bathory, who then slaughtered his "family" and presumably Mikaela, who urged Yū to run away, a fact he regrets to this day. One of Yūichirō's driving forces is his need to destroy all Wanyonya damu for what they did to his family, yet he doesn't allow revenge to consume him and instead chooses to become strong for his new family's sake. He enlisted in the Japanese Imperial Demon Army for vampire extermination, the Moon Demon Company. He is not always a good team player, but is kind and caring deep inside. His Demon Weapon is Ashuramaru (阿修羅丸?), a possession-type demon weapon which takes the form of a katana.