Kosuke Tsunoda is a participant in the Liar Game Tournament. He is eighteen years old and works as a freeter, a part-time or temporary worker. He is described as a friendly young man with light brown hair that is medium length and spiked up. He typically wears a striped, long-sleeved shirt. His demeanor is often shown to be quite nervous, especially early in the tournament.

Tsunoda first appears waiting in a large banquet hall at the start of the second round of the tournament, where he is assigned the nameplate number 8. He becomes one of the contestants who fights alongside Nao Kanzaki during that round. He remains with the same group of players through the revival round and into the third round, consistently aligning himself with Nao and her allies. His role in the story is that of a recurring supporting player who, despite his initial anxiety, continues to participate in the tournament's later stages. No direct information is available regarding his personal background before the Liar Game, his deeper motivations for joining, his specific abilities beyond being a participant, or any significant character development or key relationships beyond his association with Nao Kanzaki's group.