With her boarding house undergoing major renovations, high school student Mayama Suzu is suddenly left without a home. Thankfully, one of her mother's friends, Naoko, agrees to take her in. Although Mayama is delighted at first, her joy soon turns into anxiety when she discovers that she will be living with Naoko's son, Saeki Hotaru—her apathetic yet handsome classmate! Wanting to keep their cohabitation secret, Mayama requests that she and Saiki avoid interacting with each other at school. However, Saeki's relaxed personality constantly leaves Mayama in a nervous state. Nonetheless, as the two spend more time together under the same roof, they gradually become a bigger part of each other's daily routine, slowly deepening the bond between them.