Sueo Maruo is a third-grade male class president at his elementary school. He consistently wears thick, spiral-patterned glasses and sports a straight-cut bowl hairstyle with bangs ending just above his eyebrows. His attire features dark green elements, including a long-sleeve shirt with visible white undershirt collar and cuffs that shifts to short sleeves in summer.

Confident yet emotionally sensitive, Sueo cries easily when criticized. His primary drive is maintaining his class presidency, motivating him to craft handmade posters, deliver megaphone speeches during elections, and react intensely to perceived threats to his status. Seeking affirmation, he often interjects unexpectedly into conversations with contradictory or unusual opinions, sometimes alienating peers. He blushes or becomes flustered when receiving praise.

Academically, Sueo excels in most subjects but struggles in physical education and music. His declarations frequently end with the catchphrase "Zubari!" He deeply admires his mother, dedicating accomplishments to her with overt devotion. Among classmates, he interacts with Maruko—whom he surprises with abrupt interjections—and Hanawa.

Sueo favors foods like soba noodles, loquats, tempura, omelettes, and kashiwa-mochi while disliking natto. He cleans his ears daily and treasures his class president badge above all possessions. Born on December 31, his name "Sueo" reflects this "end of the year" origin and references artist Suehiro Maruo.