Shin Kazahara is living with his girlfriend, Sayaka Nanjo. Actually, they've been living under the same roof for a long time. Sayaka lost her parents when she was little, and Shin's parents took her in. His parents have to leave because of their jobs, so Shin and Sayaka are finally left to themselves. Sayaka teaches at the school where Shin attends. To Shin, she is a girlfriend, a sister, a mother, and also a teacher. Sayaka wonders if she should openly express her feelings to him under such circumstances. However, without his parents around, Shin experiences a new and exciting life with Sayaka.
They do have to have some rules, though. Will they live happily together, or will Shin find a new girl? The story is divided into a day part and a night part. During the day, Shin will meet up with three girls: Yui Hasuda, who grew up with Shin and really likes him, Toka Naruse, a selfish classmate, and Kisumi Takase, who is a school nurse and an advisor for Shin. At night, he'll be completely alone with Sayaka to experience many different kinds of sex. Through trying different things, Shin's techniques will vastly improve. Which will you prefer: life with Sayaka, or playing around with girls at school?