Black Zetsu

In its true form Black Zetsu is an entirely black, humanoid shape lacking hair or any visible openings, a malleable mass it can stretch and resize at will. Two yellow eyes float within it, without whites or pupils, and it moulds a jagged mouth whenever it wishes to speak. Its gaze and awareness can shift to any part of the mass, even when the body has been split apart, and it can coat another living being to seize control of them.

Bonded to White Zetsu, the pair were told apart by the Venus-flytrap shells that closed over their heads. Beneath those shells Black Zetsu bore short green hair drawn from its partner, and under the shared Akatsuki cloak the two wore bandaged legs where their bodies fused, along with the duo's green ring.

Set beside the cheerful White Zetsu, Black Zetsu is the graver and more learned half, earning the nickname Wicked Tongue for its cutting remarks. It excels at seeming trustworthy and obedient, and Akatsuki entrusted it with the secrets of the coveted Eye of the Moon Plan, yet its real allegiance stayed hidden from nearly everyone, Madara included.

Scornful of almost all it meets, it saves genuine devotion for a single figure: Kaguya, whom it calls mother and serves without limit. That loyalty ran so deep it spent untold years bending history to bring her back, dismissing the ideals of Hagoromo as absurd and betraying Madara once he had served his purpose. Naruto would later call it a snot-nosed brat too scared to ever stray from its mother's side.

Kaguya fashioned Black Zetsu in the moments before the twins Hagoromo and Hamura sealed her away as the Ten-Tails. From then on it worked to engineer her revival, goading Indra toward war with his brother Asura, rewriting Hagoromo's stone tablet to lure future generations, and steering the reincarnations of the two bloodlines toward awakening the Rinnegan. It recorded the events it witnessed, hid inside Madara's corpse, and let the dying man believe he had shaped it from his own will. Bound to White Zetsu, it served Akatsuki as a spy and body-disposal agent, reporting directly to Pain and Obito while quietly guiding the whole plan.

When Obito was drained of the tailed beasts, Black Zetsu seized his body to force the technique that resurrected Madara, then turned on Madara himself, stabbing him from behind and declaring that its will belonged to Kaguya, not to him. Spreading across his frame and feeding him the chakra of everyone caught in the Infinite Tsukuyomi, it transformed the man into the reborn princess.

In the final battle it fought at Kaguya's side, absorbing the chakra of Naruto Uzumaki and Sasuke Uchiha and advising her tactics, until Naruto severed the arm that carried it and pinned it down. As Kaguya was sealed once more within the moon, Naruto hurled Black Zetsu in after her, trapping it forever beside the mother it had always longed to stand beside. For all its scheming, its final revelation about the White Zetsu's origins gave Team 7 the clue that later warned the great nations of the wider Otsutsuki threat.