Aya's family was killed by the show's main 'bad guy,' Reiji Taketori. His sister was put into a coma, which is why he agreed to join up with Kritiker and become an assassin in the first place(he needed the money to pay for his sister's hosptial bills). Aya took his sister's name after she was put into the coma so that she would live on still even while her body was inactive. Aya is the main character of Weiß Kreuz but that's difficult to surmise during the first few episodes of the series, because the show continuously jumps back and forth between the main character's histories. There are actually more Omi-centric episodes than there are Aya-centric ones all the way through the first ten episodes, and there are only twenty-five of them! It all works out in the end, though. ^_^

Aya's personality is often considered to be cold and uncaring, and he's not very understanding of the needs of his teammates. When he first meets Ken, they actualy get into a fight because of Ken's hot temper and Aya's stand-offish nature, and poor Aya-san ends up getting the holy hell beaten out of him! But he does end up winning the respect of his teammates and becomes a strong leader of Weiß.

Yohji is the playboy and eldest member of Weiß.