I can't even find even the second department (Volume 1 whole volume)

Publisher: Kodansha
Author: Peach-Pit
Size: 128mm x 182mm
Number of books: 1
Language: Japanese
Category: Youth manga, manga
Latest publication date: 2018-07-23

Synopsis:
Shunta Hyakubuchi (nickname, Momotaro), who had a high school girl who even claimed to be a secondary department cleared the suspicion of molesting, was involved in a thought experiment called "desk theory theory" and decided to challenge the mystery hidden in everyday life.
However, he jumped off the iron bridge and acted as if he was committing suicide, and the mystery of even saying, "It looks like a high school girl but is actually an old man." Unknown high school girl and Futu's salaried worker's "don't guess" new sensation!