Nyan Koi! follows Junpei Kousaka, a second-year high school student whose severe cat allergy turns daily life into a nightmare in a family that adores cats. Things become even more awkward around Kaede Mizuno, his estranged childhood friend and crush, who is almost always surrounded by cats and by people who share her affection for them.
After Junpei carelessly kicks an empty can and decapitates a cat deity statue, he is cursed with the ability to understand cat speech. The power quickly proves to be a burden rather than a gift: he has to keep the secret hidden, because anyone who learns about it is swept into the same accident-prone bad luck that seems to follow him. With the mysterious cat Nyamsus acting as his guide, Junpei is forced into an impossible bargain. To break the curse, he must complete one hundred good deeds for cats, all while avoiding the humiliating possibility of turning into a cat himself. The result is a chaotic romantic comedy built on misunderstandings, divine mischief, and Junpei’s increasingly desperate attempts to survive both his allergy and his bad luck.