Haha to Kodomobeya Oji-san no 1￮ Nenkan no Nariyuki to, Sorekara.

At thirty, Yoshizawa Hiroto, the man still living in his childhood room...

And his mother, Yoshizawa Rie, with whom he shares a secret relationship...

How did their current relationship come to be...

This story traces their secret bond with his mother—past, present, and beyond— delving into his past, starting from his elementary school days when he attended school normally despite his introverted nature.

[From DLsite]