Yuuji Sakamoto represents Class 2-F at Fumizuki Academy as its class representative. Recognized as a child prodigy in elementary school with significantly higher academic abilities than peers like childhood friend Shouko Kirishima, he neglected studies upon entering high school, believing grades don't define personal worth. This led to his placement in the lowest-ranked Class F.

During the "Summoning Test Wars," where students battle using avatars ("Shoukanjuu") powered by test scores, Yuuji acts as Class F's primary strategist. He compensates for their low academic standing by devising intricate tactics involving psychological manipulation, inter-class conflicts, and environmental traps. These effective methods secure victories against higher-ranked classes like Class A but are often labeled underhanded or cowardly. His avatar wears a white open long-sleeved coat with a Class F badge and white pants, wielding brass knuckles. After a tournament, he gains a platinum bracelet enabling him to deploy a summoning field that restricts enemy movement at the cost of his own summoning capabilities.

Yuuji maintains a laid-back demeanor but exhibits complex traits: occasional sadism, particularly mocking best friend Akihisa Yoshii's intelligence; significant fear towards Shouko Kirishima's aggression; yet consistent protectiveness. He intervenes when others bully Akihisa and physically confronts those insulting or threatening Shouko. A strong sense of responsibility motivates him to encourage classmates academically. After Shouko defeats him in an elementary-level history test, he dedicates himself to studying, achieving substantial grade improvements.

His relationship with Shouko Kirishima is central. While harboring romantic feelings for her, he actively conceals and avoids acknowledging them publicly. Shouko's intense obsession with marrying him causes significant anxiety, prompting him to evade her advances, yet he remains deeply protective of her well-being and emotions. His bond with Akihisa Yoshii is equally significant; they communicate non-verbally and partner in schemes Yuuji frequently devises. His family includes his mother, Yukino Sakamoto.

Throughout the series, Yuuji progresses academically, eventually reaching Class 3-A. By the light novels' conclusion, he becomes President of the Disciplinary Council, with Toshimitsu Kubo as Vice President. His strategies evolve in complexity; in one instance, his plan achieves near-certain victory against Class A before external interference forces a draw.