The school's pool is out of commission, so Eriko and the girls have PE class at a nearby middle school. There they meet Momoka, Yuma's perfect and pretty little sister. Momoka decides to weave her way into the girl's hearts, pitting Yuma against the others. Finally, she tries to break Ayano up with her boyfriend, and leaves the blame with Yuma. If one of the girls can't see through Momoka's lies, her sister will be out of the group forever! Then it's a flashback to middle school, where Yuma and Eri met for the first time... as enemies!