Kouta Oyamada

Race: Human (former), Yokai (current)
Relatives: Unnamed grandfather, unnamed parents

Relatives (spoilers): Unnamed daughter (manga)

Kouta Oyamada is a first-year high schooler. Before moving to the city, he lived with his grandfather. On his first day of school, he met Chizuru Minamoto and discovered that she was a yokai.

Kouta is short, has brown hair, and silver eyes. He's shy, bears a mild personality, and is indecisive, often with Chizuru and Nozomu Ezomori.

Despite his reluctance to engage in the intimate acts Chizuru desires, Kouta bears feelings for her. They're able to fuse into a powerful being, which can only occur between a human and a kitsune when they share a deep emotional link. In this form, Kouta transforms into a black-furred, five-tailed spirit fox.

Due to his relationship and exposure to yokai, he's turned into a yokai - specifically a kitsune.

(Source: Kanokon Wiki, edited)