My Stepmom's Daughter Is My Ex

As punishment for the underwear incident, Mizuto demands Yume go on a date with him. Yume is taken aback by the sudden development, but little did she know that it was all part of Kawanami Kogures devious plan, a plan to shatter Minami Akatsukis delusional dreams of marrying Mizuto only to become Yumes doting little sister. And how else to do it but to show her that Yume only has eyes for Mizuto?

The first midterms of the school year are upon them. Once the top scoring student in the schools entrance exam and now a talented student at the top of her year, Yume is anxious to defend her position as a model student. She is displeased, however, to discover Mizuto’s relaxed approach to studying. The two later butt heads again, over something Mizuto did during their Japanese exam. Yume berates Mizuto for his actions while Mizuto retaliates in kind.

Isana is coming over to the Irido house this weekend to hang out with Mizuto. Suspecting that she may not know how to properly dress for the occasion, Yume and Akatsuki invite Isana out to go clothes shopping the day before. Unfortunately, however, every outfit she tries on ends up looking inappropriate due to the size of her breasts. Akatsuki suggests that she try on something with a softer silhouette similar to Yumes usual style, seeing this as an opportunity to pick out new clothes for Yume to try on too. Yume then reminisces about a date she had in middle school.

Its Yume and Mizutos 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. Its in situations like these that the two seem to be finding themselves reminiscing about the past more and more...

Still in the countryside visiting relatives, Yume and Mizuto head to the local summer festival together. In high spirits from getting to see him in his yukata and seeing how Madoka and Chikuma interact as siblings, Yume boldly takes his hand in hers as they walk around the festival stalls. During their outing, Yume begins to get a picture of how Mizuto was as a child. And in doing so, realizes just what his meeting her meant to him.