Seishirou Sakurazuka; an older friend of the twins (he's 25),
a kind veterinarian who's always offering to drive them places,
lend a hand in taking care of things around the apartment,
and giving information (he secretly takes his dead
patients and feed them to his demon sakura tree).
He seems to care very deeply for Subaru, but Hokuto's cuteness occasionally
gets on his nerves. He also joins in on Hokuto's teasing Subaru.
He leads a secret life kept well hidden from the twins, and eventually
he comes to represent Subaru's dark side. Subaru first met him in a
train station about a year before the story begins; Subaru was
injured and Seishirou took him home and fixed his wounds.
They also met under a sakura tree and there Seishirou told
Subaru, when he was a young boy, that they well meet again.