Negawakuha, Kimi ni.
願わくは、君に。 · ねがわくわ きみ に
est. Rough estimate based on volume count, reprints and magazine — not an official figure
Overview
Yukari Miyata would always smile and laugh, even when she got hurt or injured. He thought she was kind of annoying that way, until he found out the "reason" for her cheerful nature. Four other stories are collected in this volume, including an epilogue to the title story. (Source: Shogakukan, translated)
Source: AniList
External databases: MADB · AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections