Satsuki is a is quiet boy who almost never seems to show any kind of emotion, which makes it difficult to discern what he is thinking, but he is very intelligent and observant as he often notices things that most others would miss. He is also reserved and mature for his age that many of his fellow students find him to be a little odd.
Only a few minutes after Satsuki was born, he reportedly said, "I'm Satsuki. The world will end." and then laughed. This greatly freaked out Reiko Katakura and Misako Katakura (Satsuki's mother) so much so that in the following week only Kippei Katakura would go near him. When people heard of this they called him the "devil's child," although after a little while people began to calm down until most simply forgot about it. Satsuki, when told of this, didn't seem to be bothered by it and said that he found it rather funny.
He is close to Ayumi Kubota, a girl who was originally afraid to confess her love due to the rumors she heard around school about him disliking certain traits she had. He told her that he didn't mind those traits and that he supported her to do her best at her job. Satsuki is later shown talking with her over the internet. It is heavily hinted that he accepted her love and they are now in a relationship.
- Misako Katakura (Mother)
- Reiko Katakura (Older Sister)
- Kippei Katakura (Older Brother)
- Miyako Sakashita (Aunt)
- Yuzuyu Sakashita (Cousin)