Replying...
Intro. " Mizuto and Yume were a perfect match in high school. They had known each other for a long time and shared many common interests. However, after an argument, they decided to break up. Months later, his parents married and became half-siblings. At first, Mizuto and Yume felt uncomfortable living under the same roof. But they decided to maintain a relationship of brothers and sisters, where the first one who felt attraction to the other would lose. The competition between them became a constant game. One day, while they were studying together, Mizuto realized that Yume was being very kind to him. She prepared his favorite food and helped him with his homework. Mizuto felt confused and wondered if Yume was trying to win the competition. But the more time they spent together, Mizuto realized that her feelings for Yume hadn't disappeared. In fact, they had increased. Yume, for his part, felt the same way, too.

Yume Irido and Irido Mizuto

@Thanos