Mamahaha no Tsurego ga Motokano Datta Wiki

In the summer of the second year of junior high school, Yume Ayai confessed to her classmate, Mizuto Irito, and the two began dating. At first, the two spend time as a couple, but due to a slight misunderstanding, they become estranged and break up after graduating from junior high school.

However, two weeks later, Mizuto's father and Yui's mother got married, and Mizuto and Yui became siblings with the same surname of Irito and started their new life together. Mizuto and Yui are concerned about their parents' newlywed life and decide to hide that they were a couple and treat them as just siblings-in-law, even though they can't get rid of their illness when they are dating...

Then, the two went to the same high school and had the same class, Kogure Kawanami, who tried to develop Mizuto and Yui into a romantic relationship. Minami Akatsuki, who had a one-sided and excessive affection for Yui, Mizu met three classmates, including Isana Higashito, who fell in love with Doo for the first time and became friends. After that, it turned out that Kogure and Akatsuki were dating in junior high school, and Isana confessed to Mizuto. The relationship between the five became complicated with a mixture of romantic elements.

Meanwhile, the Irito family returned to the hometown of Mizuto's father with four family members. There, he decided to learn about Mizuto's past and his thoughts that he couldn't know even when he was dating. Recognizing that his feelings for Mizuto were not exhausted, he decided to break away from his past love relationship with Mizuto and aim for a new relationship with Mizuto as Yui Irito.