Otouto wa, Ookami.

A week after Beitofuku’s father remarries, she discovers that her new stepbrother is Aizawa Hiroki, the most popular guy at school. Though he seems like a gentleman, Hiroki is actually a notorious playboy. He tries to “capture” Beitofuku to prove that they cannot be a family. As the two adjust to their new relationship as step-siblings, Beitofuku faces the very different sides of the boy now living in her family.