The story picks up after the events of the first season of the anime. Riko and Reg, accompanied by their friends Nanachi and Prushka, have reached the 5th layer of the Abyss, known as the Sea of Corpses. They are in search of Riko’s missing mother, Lyza, who was a renowned cave raider. Their journey takes a dark turn when they encounter a group of White Whistles, elite explorers who have made significant discoveries in the Abyss.
The White Whistles are led by Bondrewd the Novel, a controversial figure known as the Lord of Dawn. He is infamous for his experiments and unorthodox methods, and it becomes evident that his motives are shrouded in darkness. Bondrewd captures Nanachi and Prushka, intending to use their unique abilities for his own twisted experiments.
Riko and Reg, driven by their unwavering determination, embark on a perilous rescue mission to save their friends. As they descend further into the Abyss, they encounter terrifying creatures, navigate treacherous terrain, and face unimaginable challenges. The film showcases the brutal reality of the Abyss, highlighting the physical and psychological toll it takes on the explorers.
Meanwhile, the true nature of the Abyss is slowly revealed. It is a place of immense power, harboring ancient artifacts and unknown entities. The Abyss has the ability to manipulate time and space, and its depths hold the key to unlocking unimaginable secrets. Riko and Reg begin to understand the true scope of their journey and the sacrifices that lie ahead.
During their quest, Riko and Reg confront Bondrewd, engaging in intense battles that test their resolve and abilities. They discover the twisted experiments conducted by Bondrewd, who seeks to merge human consciousness with the Abyss itself. The film explores themes of identity, sacrifice, and the blurred line between humanity and monstrosity.
