Kare no Shiranai Himitsu wo Irete.

Yui and Naoya have been dating for two months, but they still haven't grown accustomed to being a couple. One day, a man passing by calls out to Yui, leaving her speechless. The man is the one she lost her virginity to before she started dating Naoya, driven by curiosity about sex.

Now, the man threatens to expose her past to her boyfriend. As the secrets Yui can't tell Naoya begin to pile up inside her, she must navigate the consequences of her hidden history.