Saneatsu Narita is a fifteen-year-old high school student whose mother died in a car accident during his early childhood. His father works overseas as a business consultant, leaving Saneatsu to live independently with monthly living expenses while managing daily life alone, fostering a self-reliant nature.

Academically and athletically gifted, he stands as an all-rounder among peers but struggles significantly with computer usage. This weakness becomes a recurring point of teasing, earning him the nickname "Only Bad at Computers." Despite this, he displays sharp quick thinking and strategic planning in high-pressure situations. His personality blends determination and seriousness with a capacity for humor, often serving as the "straight man" in comedic exchanges. He exhibits strong leadership tendencies, building trust through selflessness and responsibility.

Within the death game Tasūketsu, Saneatsu emerges as a central figure after witnessing a mysterious computer message posing a yes-or-no question and awakening to a world where most people have vanished. He learns the game’s rules: daily questions determine survival, with the majority perishing each round. The last survivor earns the right to confront the Emperor, the game’s orchestrator. To combat this threat, Saneatsu utilizes hidden envelopes containing special abilities ("Special Right") and forms alliances.

His story arc begins with devising strategies to challenge the Emperor individually, uncovering betrayals like Soutarou Shinozaki’s actions. During confrontations, he makes personal sacrifices and defeats the first Emperor. A later revelation explains his survival was tied to the "stop privilege" applied to him; its lifting revives him, marking a turning point. Progressing further, he assumes formal leadership of the AEF (Anti-Emperor Force), guiding allies against threats from the third Emperor and steering the group toward new objectives.