Nin-nin is a dwarf ninja, always concealed beneath a hood. He serves as a devoted companion to protagonist Miko Mido, fulfilling roles as both comic relief and a protective figure. A pronounced voyeuristic tendency drives him to seek opportunities to observe Miko during private moments like bathing or intimate encounters. Despite this pervasive behavior, he demonstrates genuine loyalty and consistently attempts to assist Miko when she faces threats, though his efforts are occasionally hampered by his preoccupation with recording her exploits.

He embodies the "Chivalrous Pervert" archetype, balancing lecherous inclinations with a steadfast commitment to Miko's safety. While often depicted as a comedic trope, he occasionally displays unexpected competence in fulfilling his duties; these moments are typically undermined when his attention shifts to another chance for voyeurism. A recurring narrative element emphasizes his "Born Unlucky" status, marking him as the only character across all media never to achieve physical intimacy with any heroines despite persistent efforts.

Physically, he possesses yellow eyes; hair color, age, and facial features remain unspecified. His background lacks elaboration, with no information regarding origins, clan affiliations, or life prior to accompanying Miko. Throughout the series, OVAs, and spin-offs, his core traits—protective loyalty, comic relief rooted in voyeurism, and intermittent effectiveness—persist without significant evolution or deeper exploration of his personal history.