Momo Sohma is Momiji Sohma's younger sister. Unlike her brother, she is not burdened with the curse of the Zodiac spirits. After Momiji was erased from his mother's memory, his parents had Momo. To preserve Momiji's new happiness, their father forbids any interaction between Momo and Momiji. Ironically, Momo is intrigued by Momiji and seeks ways to learn more about him. She notices a striking resemblance between Momiji and their mother, who denies it.
When Momo catches Tooru trying to sneak into the Sohma estate, she shows Tooru a secret entrance. She asks Tooru to inquire if Momiji would like to be her older brother. Momo starts learning the violin, but to maintain separation, their father asks Momiji to quit, as they would have shared the same teacher otherwise. It turns out Momo saw Momiji playing and hoped that by learning the violin, they could play together.
Upon hearing from Tooru that Momo wants him as her older brother, Momiji cries tears of joy. Described as "cute" by her brother, Momo almost always stays close to her mother, likened to a baby chick always near its mother.
