Nagamasa Midori

A doctor and survival game player who, despite initially coming across as helpful, polite, and kind, actually has a brutal sadistic streak. He is the leader of the survival game team Hoshishiro, which, as of the start of the series, has won the Top Gun Combat tournament four times in a row.

He knows that Hotaru is a girl, due to the brief body check he gave her to help her find a suitable gun.

In episode 6 of the anime, it is revealed that he is the one who traumatized Toy Gun Gun's former female member and drove her to quit survival games.

It is highly implied in episode 8 of the anime that he and Masamune were friends when they were younger.