Masamune Matsuoka is a main protagonist of the series. He works as a host at the Orion Host Club, a profession that has sharpened his dynamic visual acuity and given him a polished, confident exterior. He appears as a tall, slender young man with swept blonde hair, blue eyes, and a pair of silver earrings in one ear. He is the captain and co-founder of the survival game team Toy Gun Gun, which he formed alongside his childhood friend Tooru Yukimura. Masamune is responsible for introducing the protagonist Hotaru Tachibana to the world of survival games after a misunderstanding leads her to confront him. To repay damages she caused at his workplace, he invites her to join the team, initially unaware that she is female.

Beneath his charming, playful, and somewhat flirtatious demeanor, Masamune carries deep emotional scars. His mother abandoned him when he was young, and he became suicidal until the survival game player Nagamasa introduced him to airsoft and gave him a reason to live. In the past, he invited a female teammate onto Toy Gun Gun, but she was traumatized during a tournament, a scene he helplessly witnessed. That experience left him with abandonment issues and a strict no-women policy out of a misguided desire to protect others from similar harm. His fear of being left again influences his decisions, causing him to push Hotaru away when he grows close, worried she will eventually leave him like his mother and former friends. Hotaru helps him confront his past through a one-on-one challenge, and he ultimately allows her back into the team.

As he spends more time with her, Masamune develops romantic feelings, though he struggles with them because he still does not know Hotaru is a girl. His loyalty to his teammates is fierce once trust is established, and he is deeply protective of those he considers family. On the battlefield, his abilities are formidable: he wields dual Desert Eagles and uses his exceptional kinetic vision, honed from reading people as a host, to track opponents and make split-second decisions. His role in the story is to act as the catalyst for Hotaru's entry into survival games, as a mentor and rival who must overcome his own trauma to become a stronger leader. His key relationships include his childhood friend Tooru, who provides emotional stability; the rival Nagamasa, a former close partner whose betrayal fuels Masamune's resentment; and Hotaru, whose unwavering determination forces him to grow. Throughout the series, Masamune evolves from a guarded, self-protective host into a more open and reliable teammate, learning that vulnerability does not have to lead to abandonment.