Father of Isami.
Kai who was the physicist who was researching mystery material "Ruminotait" is missing five years ago.

He is chased to Kurotengu. he binds his head with a bandage, he put on one's sunglasses, and he wears a coat to hide his identity.
He has presented Isami the brier on her birthday.
His combat skill is also high because Kai piles up the training of Rumino Ninjutsu.