Momo Karuizawa is one of the playable characters from Project Justice, acting as a major villainess in the game's story mode.
Momo is a fresh student from Gorin High School. Since Gorin specializes in sports, Momo has chosen Tennis as her specialty, displaying to have great strength despite her diminutive size and looks. However, Momo is actually an agent of Kurow Kirishima, sent by him to infiltrate Gorin and separate Shoma Sawamura from his friends.
Momo first appears being bullied by Batsu (actually Kurow in disguise), which makes the hothead Shoma immediately come to her rescue. Natsu immediately grows suspicious of her, so Momo starts hanging around Shoma to provoke Natsu, which works as the two argue and Shoma decides to go after Batsu by himself along with Momo. Though Natsu is angry at Shoma, she decides to look after him, being joined by Roberto and later Nagare. Shoma confronts the Taiyo High students on Batsu's whereabouts and later the students from Pacific High. After a brief fight, Momo leaves Shoma behind, him having served his purpose. Momo later appears in the Gedo High storyline, giving orders to the brainwashed Daigo Kazama, which makes Edge grow suspicious of Daigo's behavior.
While Natsu, Roberto and Nagare confront Kurow and Momo, Shoma arrives on the scene, rejoining with his friends after learning of Kurow's plot. As Kurow is defeated, he blames Momo for his defeat and runs away to Justice High, but Momo follows him. After Kurow is injured by Hyo Imawano, Momo attempts to rescue Kurow, but she is attacked by Hyo, who's been possessed by his father's spirit. Shoma and the others convince Momo to help them defeat Hyo, so she could help Kurow. After Kurow disappears, Momo joins Gorin High officially and becomes friends with Shoma nad the others.