The neighbor's only child and daughter: Akidzuki Yuuna...
To the protagonist who is a school teacher, she is a precious student and like a daugher to him.
One day, the protagonist's son Kouichi tells him that he and Yuuna have started dating.
The protagonist is greatly delighted by the news and promised to support their relationship as a father.
However, something occurs a few days therafter.
On an impulse, the protagonist peeks in on the pair having sex in his son's room.
The climax of Yuuna as she's embraced by his son...
The protagonist who witnessed her "female" expression for the first time realized his own lust for her.
Thinking of the pair's future, the protagonist decides to hide his lust...
However, the moment of having witnessed the sexual intercourse engraved into Yuuna's body-
-that emotion exploded, and the protagonist semi-forced her into a sexual relationship with him.
Yuuna, who doesn't want to be hated by Kouichi, says she wants to keep the fact that his father embraced her a secret...
The protagonist agrees, but continues to demand her body in accordance with his desire as a male which doesn't settle.
...Thus, their forbidden baby-making daily life has begun.