After entering high school, Yume was making an effort to change her personality and looks in an attempt to reinvent herself as a model student. It was all so far so good, but there was one thing she couldn't change about herself. She was never very athletic. On the day of the physical fitness test and body measurement check at school, a melancholy Yume is approached by Minami Akatsuki, a girl from the same class. Meanwhile, Mizuto is as disinterested as ever...

It's Mother's Day, so Yume and Mizuto go out to buy a gift together. Their mother, Yuni, is overcome with happiness to receive a gift from the two of them. Seeing how happy it made her, Mizuto wonders if it'd be nice to give their parents some time to be newlyweds together. However, there isn't much they can do for them on a high schooler's budget. So Mizuto suggests that he and Yume spend the night somewhere instead.

It's Yume and Mizuto's first summer together as stepsiblings. Their parents are unable to return home one night due to a typhoon. Now alone in the house together, trouble arises when Yume spots a certain creepy crawly in her room. On another day, Mizuto accompanies Yume clothes shopping for a swimsuit in preparation for an upcoming family trip to the countryside. It's in situations like these that the two seem to be finding themselves reminiscing about the past more and more...