Risa Ōnuma (大沼 理沙, Oonuma Risa) is an employee at the same fast food restaurant as Seiji.
Risa has red-brown curly hair, which she keeps tied up during work. Her eyes are shown to be a matching color with her hair. Risa is noted for having a well endowned-figure, with possibly the largest breasts amongst all the women involved with Seiji. She is also notably tall, as mentioned by Eri Takiguchi, she has the qualities of a model. She stands at 171 cm.
While initially being introduced as unsociable and quiet, she is later revealed to be a very shy and occasionally timid person, who is easily upset and will cry should she feel she did something wrong. Risa has been shown to be a bit quick to make decisions, and quick to judge people, having confronted Seiji many times about him leaving Yuki, who she doesn't trust at all.
Another example is when she caught Seiji dating Shou sometime later, and through despair, she was about to surrender herself to a perverted older man, until she was rescued by Tsukasa Izumi, a friend of Seiji.