Saito Kai's girlfriend. She has been secretly dating Kai since their second year of middle school, but they have kept it a secret since they first started dating. Only Sakura, Ayumi, Akihiro, and their families know about it. Because they are in the same club, even though Kai is the target of many girls, she has a lot more chances to get close than others. She eventually confesses her love to Kai. After the sports competition ends and Kasumi has a chance to be alone with Kai, Kai agrees. Because she has helped Kai for a long time, Kai has good feelings for Kasumi, but they have to keep it a secret because Kai knows that he is the target of many girls, which could cause problems for Kasumi.