On the night she said goodbye to her first boyfriend, 26-year-old librarian Mizuki wanders into a mysterious library protected by magic and a forest. Mizuki, who was scouted by the librarian [her lock] of this library, ends up signing a contract with her drunkenness. Her mission is to find the man who will be her [key] from among a kind-hearted blonde prince, a sadistic mage, and a serious priest, and find the key to her former librarian, Jay, who was cast with petrification magic. help out. She says that in order to do that, she has to meet the men who are key candidates. On top of that, the knight who protects the library also gets involved with Mizuki...