Onsokumaru leads Shinobu's ninja clan despite his appearance as a yellow, spherical shape-shifter. His name means "sonic speed ball," reflecting his typical form, though intense emotions trigger a transformation into an extremely muscular human body. As clan leader, he oversees training and missions but hides his true identity from Shinobu by wearing a fake beard when acting as headmaster, believing this deception would advance his romantic pursuits. This ruse continues throughout the series; Shinobu remains unaware even after he reveals the truth, dismissing it as another scheme.

His personality blends perversion, lechery, and greed with occasional playful friendliness. He frequently devises absurd schemes—like ordering Shinobu to steal Kaede's underwear as ninja exams—fueled by softcore pornographic fantasies about them to manipulate male ninjas or for personal pleasure. Despite his leadership, he exhibits messiness, loudness, and cheating. Male ninjas, including Sasuke, sometimes follow him but possess standards, uniting to punish transgressions like feigning illness to coerce Shinobu into bathing or targeting her younger sister Miyabi.

His relationships define his role: Shinobu remains trusting yet unaware; Kaede openly opposes his antics with physical reprimands; Miyabi, a magical summoning prodigy, consistently defeats him due to mutual animosity. His behavior leads to extreme consequences, including banishment from hell for causing excessive trouble. Across all media—original manga, anime, and sequel manga—his core traits persist without significant evolution, maintaining his role as a chaotic instigator.