放課後に乱れる姉教師と隣の部屋で喘ぐ妹 ～ 恋人になった女の子が、知り合いの嫌な男に寝取られる ～

The protagonist, Hirose Yuzuru, was an ordinary student. 
He studied and worked on his part time job like everyone else, and was content with his monotonous life.
But there was just one thing he wished to change.
He wanted to get closer with Aizawa Haruka, the woman he fell in love with from the time he enrolled in school.
“Getting into a relationship with her, a teacher, is an impossible dream,” he thought to himself resignedly.
So he continued his unchanging everyday life along with his classmate cum Haruka’s sister, Aizawa Yuuka; and the junior at his part time job, Usami Akari.

However, one day his father started talking about remarriage and his monotonous life completely changed. He started living together with the woman he yearned for, and his relationship with Yuuka (who also started living with him) and Akari began to change too.

Yuzuru looked towards his new circumstances with hope and anticipation…
but the worst possible outcome was the only thing waiting for him.