Onimaru Kunitsuna originates from Japan's Heian period as a legendary sword. He possesses a towering frame of 193 centimeters, distinguished by physical traits including an eye patch and horns. His personality is marked by a powerful protective instinct, declaring himself the sword of his founder with the vow, "I will not let anyone touch him." This dedication extends to allies, driving him to confront threats to their safety. He acts with confidence and assertiveness, guided by a strong sense of justice in his interactions and choices. While direct, his underlying motivations consistently prioritize defending the well-being of those under his protection.

His narrative appearance is confirmed within the film trilogy "Toku Touken Ranbu: Hanamaru ~Setsugetsuka~," released between May and September 2022. Details regarding his character development, interpersonal dynamics, backstory expansions, thematic roles, narrative function, relationships, or evolution within other franchise media beyond this confirmed appearance are not elaborated in the documented sources.