Katashi

Katashi is an oni, a form of yōkai, with blackish skin, red hair, and yellow eyes.

Katashi is a selfish, violent, and cruel oni who has a childish sense of violence, viewing it as a game or passtime.

Despite his stubborn personality, Katashi does learn from his experiences, and though doesn't change much in personality, becomes a better individual as he continues to show up in other character's stories.

The Green Man
Katashi first appears in The Green Man after Jack has just watched Sabina fight some ogres.

Their meeting is a verbal confrontation in which Katashi accuses Jack of needlessly meddling in other people's lives, to which Jack comebacks with Katashi's poor and selfish personality.

The meeting is a foreshadowing of Katashi's role in The Sakura Girl.

The Sakura Girl
In The Sakura Girl Katashi is the antagonist and (in his own mind) rival of Takehiro and Ales. In trying to win them both separately, he pits them against each other, ultimately becoming both of their enemies.

When his only friend Takehiro falls in love, he becomes jealous. First of Takehiro giving his time to someone else but then he takes a liking to Takehiro's woman, the Penta Girl. He tries to win her for himself. Ignorant and naive of how to deal with people and their feelings, he fails at gaining her favor and loses her and Takehiro in his efforts to pit them against each other.