Ninja-tarou is a young male ninja defined by his inherent clumsiness. He persistently introduces himself with grandiose titles like "Musashi's first disciple" and "the ninja of ninjas," projecting aspirations of great significance. However, his actions consistently fail to live up to these claims of mastery. He struggles with combat and stealth, displaying skill levels comparable to Sasuke Sarutobi, a character transformed into a "ninja monkey," firmly establishing Ninja-tarou as a comically inept figure. He relentlessly attaches himself to protagonist Musashi Miyamoto, attempting to validate his self-declared discipleship within the main narrative.

No background details concerning his origin, lineage, or formative experiences are provided. Ninja-tarou exhibits no character development, evolution in abilities, or deepened relationships throughout the series. His static role remains that of a source of lighthearted mishaps and exaggerated failures, primarily during encounters with supernatural adversaries called Ayakashi.