Yuuta has his two elder sisters, Chiyo and Chinatsu.

This story takes place in the days leading up to their school's School Festival. One day, Chinatsu overhears Yuuta being invited to a soccer match by his best friend, for the purpose of "curing his sis-com".

After they return home, as Yuuta is folding the laundry, he comes across a pair of racy panties! As he holds the panties in his hand, pondering its owner, Chinatsu creeps up on him from behind...

When he comes to, Yuuta finds Chinatsu sucking his dick. When he protests, Chinatsu tears up, explaining that she's jealous of how close he is to Chiyo. When Yuuta hears that, he's relieved of his preconception that Chinatsu dislikes him. However, at that moment, Chiyo also appears...