The protagonist, Otonashi Sumiya, and the heroine, Suzumori Mei, have known each other since childhood. Their houses are next to each other, and they have grown up together as if they were brother and sister.

But their relationship changes drastically when Mei confesses her feelings for Sumiya.

"Erotic temptation".

She began to make sexual advances toward him at every opportunity.

"I'll make you fall in love with me for sure!"

Sumiya thought that as childhood friends, they would always be like siblings. However, his feelings gradually change under Mei's daily appeals to him.

"As her childhood friend, I thought I knew everything about her."

Seeing her expressions for the first time, knowing her gestures for the first time, and experiencing her emotions for the first time.

What will happen between the two as they move forward in a relationship that goes beyond childhood friendship?

[Translated from official website]