On a rainy day, the kind-hearted Nanamori Ryotaro finds a mysterious young man named Nao, shivering and soaked to the skin. Nao introduces himself as「the cat that Ryotaro once saved」and begs to stay by his side to repay the favor. Ryotaro is confused, but unable to leave Nao alone, and so they begin a strange life together. Nao is as innocent as a cat, good at being cuddly, and sometimes approaches Ryotaro in a devilish manner, and Ryotaro gradually finds himself at her mercy, both mentally and physically. But Nao has a secret he cannot tell!? This is a slightly clumsy love story between the two, full of secrets, that begins with Nao wanting to repay a favor!