Bondrewd's smile never wavers while he systematically dismantles everything you thought was safe about this world. The film commits fully to the horror of descent, not just physical, but moral, and the animation renders every devastating choice in nauseating clarity. By the end, you understand why Nanachi survived, which means you understand what surviving cost, and the movie doesn't look away from that price for a single frame.

Riko and Reg, now traveling with their new friend Nanachi, head down into the Sea of Corpses, the fifth layer of the Abyss. It is the deepest point from which anyone can come back still human. There they meet Bondrewd, a masked scientist and legendary White Whistle who shaped Nanachi's painful childhood. He treats the children as honored guests, but his grim laboratory stands as the last checkpoint before the depths below, and he will not let them through for free. His one apparent weakness is Prushka, a bold girl who calls herself his daughter. The children befriend her as they look for a way to reach the sixth layer. The film mixes adventure and fantasy with psychological horror.