Nagamasa is the leader of the survival game team Hoshishiro, which is the name of the hospital he works as a doctor at along with his teammates Fujimon and Ichi. He initially appears to be a very kind man, but he is the object of Tooru and Masamune's resentment due to what took place in the past. It is revealed that he beat up two former Toy Gun Gun players, but it was all within the rules of TGC. He and Masamune used to be close partners, but after being told by another survival game player that Masamune was also a strong vanguard, Nagamasa was convinced to end their partnership. Although brutal during survival games, Nagamasa is known to show kindness outside of it. He knows that Hotaru is a girl but kept a secret though it ended being a blackmail for Hotaru.