He has a spin-off manga called Ichinichi Koshitsuroku Numakawa were he is the main protagonist.
Tobaku Hakairoku Kaiji
Ichinichi Gaishutsuroku Hanchou
He plays a supporting role in the spinoff along with Isawa.
He is not used to going outside the underground labor camp for a day and struggles on how to enjoy his time outside. Ōtsuki decides to teach him how to enjoy the day properly.
Ichinichi Koshitsuroku Numakawa
Numakawa buys a one day ticket for an appartment. He grows bored since he is still underground. He sings Karoke and gets heared by his fellow miners.