Mc wants to win over his precious childhood friend’s heart. But because of his past, his childhood friend, Rio, only sees him as a little brother. Mc used to be clinging on her so much, he even calls her onee-chan. He had a thought of marrying Rio and having happy family life with her. He realized that he can’t confess to Rio with his current self, so he studied hard so he can land a good job and become the man she love. But Rio already had her feeling for someone. Just like Haruto to Rio, Rio used to stuck to someone called Kaito. The guy who used to hang out with them. Rio doesn’t want to make Haruto sad so they secretly keep their relationship and let the time flows without Haruto knowing the reality.