18+ Tedama ni Toritai Kurokiya-san

Kurokiya Ruu is on the verge of repeating a year so her childhood friend Tadashi Tadao (whose name literally means straightforward man) steps up to teach her. However, they end up not getting any studying done as she uses this situation to try and seduce him at every turn. The story of a girl who wants to get her crush flustered and the straightforward guy who won't get embarrassed.