Onee-chan no Midori-kunお姉ちゃんの翠くん; Midori Loves My Sister

The manga centers on Sui, a girl in her third year of junior high. She doesn't really get along with her older sister's boyfriend, Midori-kun, since he always treats her like a kid and makes fun of her. But Midori-kun is suddenly asked to be Sui's home tutor.