Boruto Two Blue Vortex Manga - Ch 81

Koji's eyes widen. "The key Saisei spoke of... it's not a weapon. It's a person. Someone who shouldn't exist in this timeline. Someone who is neither human nor Otsutsuki. Boruto... you have a sibling."

"Father didn't seal me away. He hid me. Because if Jura finds me... the Two Blue Vortex becomes a black hole." Boruto Two Blue Vortex Manga Ch 81

Flashback to earlier that day. Shikamaru (now the Eighth Hokage) explains to Sarada and Mitsuki that before Naruto and Hinata were sealed away, Naruto left a final contingency: a key to a seal that predates Kaguya, hidden in Uzushio. "Boruto and Kawaki both have Otsutsuki powers," Shikamaru says. "But the Ten Tails' original husk—the one Jura came from—has a weakness. A 'Seal of Origin' that can reset its will to zero. Without that, Boruto's plan to save your father is just suicide." Koji's eyes widen

A single panel. Deep underground, in a forgotten Otsutsuki dimension, a young girl with Naruto's whisker marks and Kaguya's Byakugan opens her eyes. She is trapped in a crystal, a shinobi headband at her feet—the symbol of the Rain village crossed out. Beside her, a journal with a single entry: It's a person

The chapter opens not in Konoha, but in the desolate ruins of the Land of Whirlpools (Uzushio). Sarada, Mitsuki, and a small covert team from the Leaf stand before a massive, ancient torii gate, half-submerged in the sea. Sarada activates her Sharingan. "The residual chakra here isn't just Uzumaki," she says. "It's Claw Mark energy—but older. More primal."