He's one of Ichigo and co's friend. He has a boyish face and speaks in a gentle manner. It seems to give Keigo the creeps at times whenever he speaks respectfully towards him. Also, Mizuiro has fondness for older women, one thing Ichigo revealed in the beginning of the series to Rukia.

Later in the series, along with Tatsuki and Keigo. He's also fully endowed of his spiritual awareness and was able to witness the departure of Ishida, Chad and Ichigo to Hueco Mundo.

Though Mizuiro has no trouble getting several girls at once (which makes Keigo extremely jealous), he seems to have suffered from lonely depression before meeting Ichigo and Keigo. He hardly ever sees his parents because of their busy schedules, which causes him to have a inverted personality. Though Keigo was Mizuiro's first real friend, Keigo later admits that Ichigo was the first person that Mizuiro ever really opened up to.