Seishirou Sakurazuka
, 桜塚星史郎
Dr. Seishirou of Tokyo Babylon is a compassionate animal doctor who often jokes with Hokuto and Subaru about their potential union, although he quickly dismisses the idea as Subaru becomes flustered with embarrassment.
Spoilers:
Seishirou is actually the Sakurazukamori (powerful assasin onmyouji), or the "Sakura Assassin" whose signature is cherry blossoms and the symbol of an inverted pentagram. He made a bet with Subaru long ago, which entails the climax of the series.
Seishirou is one of the Dragons of Earth, where he reveales his true self as a cold-hearted assassin who killed Subarus twin sister Hokuto. In their final battle at Rainbow Bridge, Seishirou arranges for Subaru to kill him realizing who really won the bet.
