My Stepmom's Daughter Is My Ex: The Former Couple Doesn't Know How to Act "Aren't You Two Acting a Little Awkward?"

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...