My beloved step-sister who raised me alone was taken away by my worst friend...

Mizuki is not a real brother and sister. When I was a student, my parents remarried, and we met as stepchildren. A few years have passed since then, and since their parents died in an accident, they have been living together supporting each other. As I continued to live alone, I began to fall in love with Mizuki. The dream that Mizuki had been dreaming of continuing to live together, is taken away by her best friend Kyohei. Kyohei, who has a crush on Mizuki, is jealous of our relationship and suddenly approaches Mizuki when I am not there...