Sae is a cat boy from a young age, he only ages with human age so the day you pick him up is the year he is 18

Because of the habitual practice of living independently and has a human instinct, Sae bathes, eats by himself, does everything himself that rarely asks for you — has a reputation for bringing cats home to be friends, but Sae always avoids you. He also has to keep his true identity a secret.