Kouta Tsuchiya, nicknamed Muttsurini or Voyeur, is a student in Class 2-F of Fumizuki Academy, recognizable by his blue-gray hair, blue eyes, and perpetually weary expression. Taciturn and anti-social, a reputation as a pervert fuels his notoriety, marked by a tireless pursuit of risqué snapshots—especially panty shots—via the camera he carries everywhere. Dubbed the "Silent Ninja Pervert" for his stealthy methods, his classmates humorously tolerate his antics, with Akihisa Yoshii regularly buying his clandestine photos.

Academically inept in most subjects, Kouta excels in Health and Physical Education, his expertise surpassing even instructors. This mastery empowers his summon: a ninja-themed combatant armed with a camera and kodachi swords. The avatar adapts to scenarios like a vampire guise during a Test of Courage or a seasoned photographer in a futuristic battle, mirroring Kouta’s unwavering focus on erotic imagery.

His tragic past includes losing two older brothers and a younger sister to poisoned imitation food. Despite his aloofness, he remains integral to Class 2-F’s tight-knit circle, alongside Akihisa, Yuuji Sakamoto, and Mizuki Himeji. A recurring gag highlights his susceptibility to extreme nosebleeds when confronted with suggestive thoughts or interactions with Aiko Kudou, whose teasing often flusters him. These reactions subtly suggest unspoken romantic tension, though he masks it with embarrassment.

Notable growth includes cross-dressing in a special episode, where his convincing disguise secures a contest victory, and incremental resilience against Aiko’s provocations—delaying a nosebleed for 28 seconds in one instance. His stealth and reconnaissance skills prove vital to class strategies, offsetting his comedic perversion with tactical value. While his core traits endure, subtle shifts in group dynamics and personal interactions hint at layered development beneath his enduring persona.