Onee-chan no Midori-kun

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. (From ANN)

https://www.cmoa.jp/search/result/?word=%E3%81%8A%E5%A7%89%E3%81%A1%E3%82%83%E3%82%93%E3%81%AE%E7%BF%A0%E3%81%8F%E3%82%93