The kabocha wine manga

The Kabocha Wine summary:

Transfer student, Aoba Shunsuke, arrived at Sunshine School only to find the premises empty. He was secretly gleeful to be the first to reach the school, oblivious to the fact that it was Foundation Day and a rest day for the institution. At that moment, a big-sized "L"(Eru) beauty by the name of Natsumi appeared before him and the two of them hit off together even though Shunsuke was so much smaller than her. Shunsuke's mother runs a women's apparel busines but the shop is in need of manpower. Shunsuke offers to help out at the shop but fumbles a lot because he does not know how to interact with the ladies. Eru decides to step in and help out around the shop and this pleases Shunsuke's mother. This is a romance story that shares the joys and woes of the "SL" combi between Shunsuke and Eru. The Kabocha Wine won the 1983 Kodansha Manga award for shounen.