Hatori Sohma is the Dragon of the Zodiac in the fictional manga and anime by Natsuki Takaya. Although he is the dragon zodiac, he does not transform into an actual dragon, but rather an eight-centimeter long seahorse, which, in Japanese, means literally 'baby dragon'. Hatori is very self-concious about this. However, Shigure thinks that this is a sign that the curse is weakening.
Hatori is about 27 or 28, like his two best friends, Shigure Sohma and Ayame Sohma. Hatori is a great contrast to Shigure and Ayame's playful nature, Hatori himself being rather somber and stern. He is the only person that Shigure trusts to tell his schemes, and he is the only person who can control Ayame's worst behaviour.
Hatori is the Sohma family's personal doctor, and he also has the ability to supress the memories of those who find out about the curse and Akito Sohma orders for their memories to be supressed, such as the time when Yuki Sohma was young and a girl hugged him, and when he transformed a whole group of people witnessed it, which he feels guilty for because Yuki had begged him not to because they had been his first friends (manga only).
Hatori is a kind person, and in the second volume of the manga, when he is first introduced, he invites Tohru to his house to talk to him. He tells her that she should leave Shigure and Yuki and Kyo and get away from the Sohmas so that she is not hurt.
Hatori warning Tohru about this is because of something that happened before, when Hatori had a girlfriend. Her name was Kana, and she was his assistant. She was part of the 'outer family' of the Sohmas. The two fell in love, and they wanted to be married. When Kana found out about the curse, she said she didn't care. When Tohru first sees Hatori transform, Hatori notes that her reaction was the same as Kana's was. They were very happy together, but when they went to Akito to ask permission to marry, Akito flew into a rage, claiming that Kana was unable to break the curse, so why should she give Hatori to her, she didn't need her. While Akito was angry, she hurt Hatori, hurt his eye, so now he is blind in his left eye. Akito blames Kana, saying to her, "If Hatori goes blind, it's your fault!"
Afterwards, Kana blamed herself for what happened to Hatori. She couldn't stop crying, she was sick - heartsick. So much, that Hatori erased her memory to free her from it. While Hatori was erasing her memory, she told him that she was sorry, sorry that she couldn't protect him. Hatori was thinking that he should be the sorry one, that he couldn't protect her, and despite that, she thought of only him till the very end.
Hatori only wanted her to be happy. And later, he saw her again, although she didn't notice him. She was with her friends, and Hatori learned that she was happy, as she was about to marry someone else. Because she was happy, he was happy. In the manga, she married a young man not related to the Sohmas; her long-time best friend Mayuko Shiraki attended the wedding, but Hatori chose not to go, fearing that his presence would only cause trouble.
In the manga only, after Kana is married, Shigure manipulates Hatori into meeting Kana's best friend, Mayuko Shiraki, who had always secretly liked him, but was happy for him and Kana when they were together. In the last chapter of the manga, Hatori appears to be dating Mayuko (who is also Yuki, Tohru, Saki, Arisa and Kyo's homeroom teacher), and invites her on an Okinawa holiday.