Boku no Papa ni Natte Kudasai
僕のパパになってください · ぼく の ぱぱ に なって ください
est. Rough estimate based on volume count, reprints and magazine — not an official figure
Overview
Haruki Nara (30), a salaryman who is busy with his work, being overly demanding on himself and on others. Only to a stranger named Haida, a middle-aged man whom he calls "Papa," can he show his true self. At Haida's suggestion, the two experience what Haruki had wanted to do as a child... (Source: Pixiv Comics, translated)
Source: AniList
External databases: MADB · AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections