Kankuro Nishiyama is a central figure in the comedic conflicts of his hometown, a young man whose life has been largely defined by his one-sided rivalry with a much stronger and more oblivious opponent. He is twenty-four years old and has just returned to his hometown after spending four years in college. His primary reason for coming back is a deeply personal one: to seek revenge against Miki Onimaru, a younger woman who brutally bullied him throughout his childhood and elementary school years. His experiences with Miki left him with a profound psychological scar, and he believes that the only way to free himself from his traumatic past and finally mature as an adult is to defeat her and earn her respect.

Personality-wise, Kankuro is characterized by his intense, single-minded determination, which often borders on foolishness. He is somewhat thickheaded and frequently fails to account for Miki's overwhelming strength or her unexpected resourcefulness when he schemes against her. Despite his age and college education, his emotional development seems to have stalled, leaving him trapped in the mindset of a bullied child who cannot move forward until he has settled an old score. He is also notably poor, supporting himself through various part-time jobs and odd ends. Adding to his constant frustration is a very specific indignity: Miki can never remember his name, addressing him with generic nicknames instead, which only fuels his grudge. He has a distinctive verbal tic, often adding the sound "nya" to the end of his sentences.

Kankuro's role in the story is that of the persistent, often hapless rival. He serves as a regular antagonist to Miki, constantly challenging her to a fight only to be swiftly and comically defeated each time. His obsession creates a dynamic of a "cycle of revenge," where he repeatedly concocts new plans and schemes to gain an advantage, all of which inevitably fail against Miki's superhuman abilities. Although his physical capabilities are actually above average for a normal person, he is no match for Miki, which makes his quest both tragic and humorous. Despite his fixation, Miki herself does not consider him a true rival, viewing him more as a persistent nuisance or a "bit-part bad guy". This disconnect is central to his character.

In terms of key relationships, his entire world revolves around his antagonistic connection with Miki Onimaru. While he sees her as the villain who ruined his youth, their violent interactions are also the primary lens through which he engages with the world. He has been known to form temporary alliances with other characters who share his disdain for Miki, such as Megumi Kannazuki, the owner of a local bakery and Miki's other rival. Outside of his obsession, he is shown to be a hardworking individual. When he focuses on honest work, he proves to be surprisingly competent, once helping at a ramen shop with such skill that business improved markedly. In the sequel series, his character shows a degree of development; he gets a job at a supermarket called Steel Frame, working under a disguise as a person in a shark suit. This job provides him with a new sense of purpose and a connection to others, allowing him to move slightly beyond his all-consuming revenge quest.

Regarding notable abilities, Kankuro is not weak by normal standards. He is presented as a first-class worker with genuine skill and a respectable demeanor when not focused on Miki. He is resourceful and exhibits a hot-blooded sincerity in his various part-time jobs. However, his combat abilities are completely outclassed by the superhuman strength of Miki, making his fighting style less about effectiveness and more about sheer stubborn persistence. His true talent lies not in fighting, but in his surprising competence at any honest task he puts his mind to, whether working at a ramen shop, a supermarket, or a horse grooming service.