Kunihiro Yamanbagiri is an uchigatana forged as a replica of the divine sword "Yamanbagiri," burdened by a complex about his status as a copy rather than an original. He reacts defensively to being labeled an "imposter," "wannabe," or "fake," yet firmly asserts his identity as the masterpiece of his creator, Kunihiro. He is Kunihiro's sole work in the Kotou ("old sword") style, commissioned by an Ashikaga lord captivated by the original Yamanbagiri's beauty. Despite his self-perceived flaws, he exhibits significant combat prowess and leadership ability, resulting in appointments like captain of the First Unit or leader of the Fifth Team during missions. His competence exists alongside a cynical attitude and complicated approaches to his duties.

He possesses blonde hair and green eyes, standing 172 cm tall. To deflect attention and avoid being called beautiful, he deliberately chooses tattered or shabby clothing, reflecting his discomfort with aesthetic admiration and broader struggles with identity and validation. He operates by deeply personal convictions, distrusting generalized trust and basing loyalty on specific individuals who affirm his worth. He thrives only under a master who enables him to "shine as a masterpiece," underscoring his need for selective recognition.

Across official media, including anime, movies, and stage plays, Yamanbagiri Kunihiri is consistently a central figure. He frequently partners with Mikazuki Munechika, especially in early stage plays, where their dynamic explores legacy and duty. His storylines involve protecting historical timelines from alteration by antagonistic forces, a mission demanding collaboration with other anthropomorphized swords stationed at bases like the Honmaru Citadel. These narratives chart his journey toward reconciling his replica status with his inherent value as a warrior, focusing on balancing duty with personal identity, confronting the emotional weight of history, and gradually accepting his unique position as both a replica and a masterpiece.