If you want to see more of kumagawa you have to read the manga Anime went out of butget there is only 1 side episode with him sadly him getting up again is a reference to his ability "All Fiction" he can turn things into Fiction aka undo them including damage he took the hole Loser thing is kinda his outlook on live and himself
that mirror match makes me wonder how the universe would handle two kumagawas fighting, since kumagawa by nature is destined to lose no matter what. wouldn't be surprised if it just ended in a draw every time
Kumagawa power is all fiction is where he erase anything he wants and also his other ability called bookmaker if his screws touch you you will become a human with no power