The office lady (OL) Sumire is bad at dealing with men because she was raised surrounded mostly by women.
Her experience of not having a boyfriend is equal to her age! If that same Sumire wants to experience men once... then it has to be sex!

Sumire has set the hurdle high for someone who has trouble handling men. When she asks Tachibana, who is the only man she can speak to normally, he says he'll have sex with her with some conditions?