Kouta Tsuchiya, nicknamed Muttsurini or Voyeur, is a reserved Class 2-F student at Fumizuki Academy, infamous as the “Silent Ninja Pervert” for covertly collecting and selling risqué material like panty shots or bust-size data to peers such as Akihisa Yoshii. His antisocial exterior clashes with extreme shyness, manifesting in comically violent nosebleeds when provoked by suggestive situations, particularly during teasing from Aiko Kudou or interactions with female classmates.

Academically, he barely outperforms Akihisa, excelling only in Health and Physical Education due to his encyclopedic knowledge of sexual topics. This expertise shapes his ninja-themed Shoukanjuu, armed with kodachi swords and a camera for stealth reconnaissance. The avatar adapts to scenarios—transforming into a vampire during the Test of Courage arc to mirror blood-themed humor or a reluctant professional photographer in a hypothetical future, clashing with his preference for adult-content creation.

His family—two older brothers and a younger sister—perished after consuming a toxic imitation of Mizuki Himeji’s cooking. Despite his perverse habits, he shares close bonds with Akihisa, Yuuji Sakamoto, and Class 2-F allies, contributing stealth tactics during Exam Summoning Battles. Aiko’s provocations spark exaggerated reactions, underscoring a dynamic of mutual teasing and latent romantic tension.

Recurring gags include his futile attempts to photograph Minami Shimada’s wrestling assaults on Akihisa, always foiled by obstructed angles. A special episode highlights his cross-dressing prowess, allowing him to pose as a striking yet socially awkward “mysterious beauty.” While his core traits remain static, later episodes show subtle growth, such as enduring Aiko’s teasing longer, hinting at incremental desensitization.