Satori

Roughly the bulk of Gamabunta or the Eight-Tails, the winged beast carries no head; a jawful of bone juts instead from a mouth set in its chest, and black feathers sheathe the body. Its tail runs long and slender, and the clawed limbs taper so thin they read as bare bone barely wrapped in skin.

Satori flings its own feathers and giant orbs at brutal speed, the feathers punching clean through a target while the orbs detonate on impact. Its size belies real agility in the air. A property drawn from the Box of Ultimate Bliss lets its body register fear and bloodlust in an enemy, so on pure instinct it veers clear of nearly every blow thrown by anyone who dreads it or means to kill it. That sense, sharpened by fast reflexes, let it slip past everything Naruto and the Konoha 11 flung its way, even with Naruto in Sage Mode. Anyone who claims the demon's power has their mind twisted in return.

By Gamabunta's account, the Box of Ultimate Bliss opens, drives, and closes around Satori, yet the creature's story stays largely unknown. Its roots run as far back as the age of the Six Paths Sage, and it serves only as the Box's puppet: step into the Box and walk back out, and you rise again as Satori's host, handed its powers while your mind rots, whereupon you begin flinging others inside.

In Blood Prison, Mui pleads with the Box to return his son Muku, and the boy emerges only to cut his father down. The sight of his childhood friend Ryūzetsu throws Muku into turmoil, and he warps into Satori, flinging inmates and four Hōzuki Castle councillors into the Box before Naruto and his allies close in. Satori runs a claw through the bellies of Naruto and Ryūzetsu, but the pair use the wound to hold it fast so Mui can bind it with his Fire Release, the Great Fire Heavenly Prison, leaving it exposed for Naruto to strike with the Wind Release: Rasenshuriken. Muku, briefly himself again, is seized once more and slays Mui, then turns the Demon Lantern on his own body to spring the sealing prison, dying so that Satori is forced back into the Box. Cast into the whirlpools beyond Hōzuki Castle, the sealed Box is left where none can ever open it.