Makes short
Kai is Saya's adopted elder brother if you can go beyond that he is only human.
Kai beings loving Saya but Saya doesn’t return his feelings for she is drenched in blood and bealives her only purpose is to kill diva.
After Saya kills Diva, he is able to convince her to continue living. Saya and Kai return to Okinawa and reopen their late father's restaurant. A month later, Saya goes into her 30 year hibernation cycle and Kai puts her in the family crypt to sleep. He keeps his promise to Saya and he raises Diva's daughters as though they were his own.

It’s sort of a said story, would be nice if they made a mini conclusion story.