Satsuki is Kippei's younger brother. Even though he's younger than Kippei, he is more centered than Kippei. He's quiet and kind, and usually just stays in the background. Although he says he's not very good with kids, he gets along with Yuzuyu very well.

Katakura Kippei is in every way a high school playboy. Spending his days flirting with any female he can see, responsibility is the last thing on his mind. Life takes an unexpected turn for him as one day he returns home to find himself with the fulltime task of caring for his 5 year old cousin. Kippei's aunt Miyako had disappeared, appearing to have abandoned his cousin, Yuzuyu. With Kippei's lack of responsibility and knowledge of childcare and Yuzuyu's injured heart with the disappearance of her mother, their time together is in for a bumpy ride. Based on the manga by Maki Youko.

Kippei Katakura is a 17-year-old playboy who spends his time chasing girls, careless of their feelings. But when his 5-year-old cousin Yuzuyu comes to live with his family after her mother's sudden disappearance, Kippei is put in charge of taking care of her. As Kippei gets to know Yuzuyu and starts to understand how she feels, he also begins to realize that all girls were like Yuzuyu once...
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(Source: Viz Media)

Satsuki Katakura