He is the Rabbit of the Chinese Zodiac. Momiji is a cute, cheerful, and childlike boy, who is easily mistaken as an elementary school student when he is actually in high school. Despite his cheerful attitude, he hides a sad family life behind his smile. Personality will have some spoilers for Fruits Basket (2019).

Momiji is an extremely bubbly, cheerful, fun, and childish boy who is always seen with a smile. He sometimes acts like a wild child since he has no real adult supervision aside from Hatori. But he is also shown to be a kind, helpful, and social person who easily gets along with others. He is very affectionate, loves hugging people, and has little sense of personal space, especially towards Tohru, as his excitement at meeting a female outside of the zodiac has led him to hug her in public places, carefree to the fact that people might see his transformation. He also continues to glomp Tohru as a greeting later in the story as well. At the same time, Momiji possesses great empathy and intuition about others. He is emotionally strong and wise beyond his years, evidenced when he told the story of the foolish traveler and about his family situation to Tohru. He occasionally displays seriousness, though it is usually quickly followed with childish antics. It is implied that he is more mature and somber than he looks, and puts on a cheerful, childish facade― which in turn is heavily implied because of his situation with his own mother. He is also shown to be courageous and able to stand up for people he loves.

As a member of the zodiac, Momiji is cursed to turn into his animal - the rabbit - whenever someone of the opposite gender embraces him. He will also transform if he is particularly stressed or weak.