Seike Tadatsugu

"I'll let you fully enjoy the power of the head of the Seike family."

Yuu's father. Ever since his wife left him and his son alongside his elder son, he's been working hard to raise his younger son so that he would not feel lonely. Thanks to the arrival of Kuro and Tenkai, he feels less lonely, so he is very grateful.

The head of the Seike family. He loves his son and calls him "Yuu-chan," whether they're at home or outside. He's hated for it, but he doesn't care. He has a good relationship with his family and seems to be in regular contact with Kai, his eldest son.