Takashima Hiromi manga
Twenty-nine-year old Kurose Kazumi is a programmer in a eroge company and has played plenty of galges when he was younger, but he's completely uninterested in young girls. A chance encounter changes that when he meets a middle schooler who suddenly says she can't date him, but he realizes how cute she is and wants to keep her with him.
Yamada is the plant appointee; tending the school's garden of flowers on her own. She isn't the slightest bit athletic, she's actually quite clumsy. However, that doesn't stop her from having feelings for the star athlete in the class next-door, Kase-san. Slightly shy, Yamada is reluctant about her feelings for the enthusiastic Kase-san. Slowly but surely, the pair are helping each other to grow in confidence for both themselves and their budding relationship, each blush and brush of the hand at a time.