Boku no Papa ni Natte Kudasai

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)