Masamune works as a Host at the Orion Host Club. He is responsible for introducing Hotaru to the world of "Survival Games". He, together with his childhood friend, Touru form an alliance called the "Toy ☆ Gun Gun Team". He is unaware of the fact that Hotaru is actually a girl. He invites her to form a survival game team with him on the condition that she repay the damages caused to the club by being a member.
It is revealed in episode 5 that Toy ☆ Gun Gun used to have a girl member, whom Masamune had invited. However, she was traumatized by a particularly brutal defeat in the Top Gun Combat tournament, and she quit survival games as a result. Although she didn't verbally blame him, Masamune, who watched the whole thing but was pinned down and unable to help, was left traumatized by the experience as well, leading to his current policy against letting girls join his team, as he doesn't want to put them in potentially dangerous situations.