Ao Arc

An arc of the Boruto: Naruto Next Generations franchise, also called the Vessel Arc in its anime form and first labeled the Kara Arc during serialization. It stretches across volumes 5 and 6, adapting chapters 16 through 23 and episodes 178 to 187. The manga positions it after the Mujina Bandits Arc, the anime after the Kara Actuation Arc, and both feed into the Kawaki Arc. Its central threads are the shadowy group Kara and the enhanced swordsman Ao.

Summoned by Jigen, the Inners of Kara learn their vessel has been lost, and Koji volunteers to gather data on the new Scientific Ninja Tools before burning the traitorous Victor alive. In Konoha, Boruto spars with Naruto and is stunned to discover his father's prosthetic hand is itself a Scientific Ninja Tool, one Katasuke built after the Ōtsutsuki battle. Sasuke reminds the boy that such devices are neither good nor evil, only shaped by their wielder. Team 7 is tasked with escorting Katasuke and the prosthetic to a research lab, and aboard the Thunder train they meet Ao, a former Kirigakure shinobi kept alive by scientific enhancements, who quietly lifts intelligence from Katasuke under a genjutsu for Koji.

At the facility Team 7 tests various tools alongside Sumire, Nue, and Akita Inuzuka, until Naruto loses contact with Konohamaru and Mugino near a downed airship. Sent to check on them, the team is ambushed by autonomous puppets, which Katasuke neutralizes with an absorption sphere. Ao then corners the group in a cave, mortally wounds Mugino, and hunts the survivors, vowing to kill them all. Rallying around a plan that leans on the very tools Boruto once scorned, the genin bait Ao into draining himself dry, and Boruto lands a Rasengan by cancelling out the man's absorption with a jutsu absorption arm of his own.

The two duel across the ruins, Boruto shredding Ao's remote drones with explosive tags before wrecking his weaponized arm. Spared and goaded to strike a killing blow, Boruto instead argues that even Ao's tools can serve good ends and urges him to keep living. Ao calls out to Koji, who drops a huge summoned toad onto him; the swordsman spends his final effort shoving Boruto to safety and is crushed beneath it.

Koji seals the shinobi in place and moves to incinerate them, but Boruto's Kāma flares to life, swallowing the flames meant for Konohamaru and marking the boy as Momoshiki's chosen. Satisfied by the display, Koji withdraws, having noted that Mitsuki's restraint betrays him as Orochimaru's child. The group buries Ao and prepares to head home. Back at Kara's base, Delta pins her suspicion of the traitor squarely on Koji. Before the team departs, Chamaru draws their attention to an unconscious boy, Kawaki, who carries the very same mark as Boruto.