In a world inhabited by demons, cyclopes, and other fantastic creatures, humans stand apart as the outcasts. Quick to anger, the human race engaged in a war that all but wiped them out. The few humans that remain are seen as a delicacy, serving no purpose but to be hunted down and eaten. One day, a golem—a wandering protector of nature—encounters a lone human child while patrolling. Inspired by her enthusiasm, he takes the girl, named Somali, under his wing. Together, the duo embarks on a journey to find Somali's parents and bring her home.

Five years ago, gravity-defying bubbles with mysterious powers rained down upon the earth. After a huge explosion of uncertain origin, Tokyo became ground zero, with the city being enclosed in a gigantic bubble. As a result of this Bubble Fall phenomenon, the metropolis that was once the capital of Japan drowned in a gravity-bending sea; the government declared it a prohibited zone, and the residents abandoned it. Children orphaned by the Bubble Fall now squat illegally in Tokyo, partaking in dangerous parkour team battles across the city's dilapidated buildings. Hibiki—a talented ace in these games with the ability to jump between bubbles—claims he can hear sounds from the Tokyo Tower. Determined to uncover its mysteries, he sets off toward the source, but he falls into the waters below. A strange girl, whom he later nicknames Uta, saves him. But little does Hibiki know that Uta's appearance in his life will reveal the secrets behind the disastrous event that changed their world forever.

Dressed in a conspicuous outfit and armed with an eccentric spirit, Hina Satou goes around insisting that she is the Asgardian god Odin. When she crosses paths with a boy named Youta Narukami, she uses her precognition abilities to warn him about an impending catastrophe threatening the end of the world. But being a teenager preoccupied with his problems, Youta finds it hard to believe such a preposterous claim. Somehow forced to tag along with her antics, he witnesses the effectiveness of Hina's skills with his own eyes and realizes that she truly is capable of divination. Nevertheless, despite her persistence in being a god, Hina is still a child who desires to see and experience the wonders life has to offer. With the world ending in 30 days, Hina, Youta, and their friends venture forward to create lasting memories they will cherish forever.

Second part of Dungeon ni Deai wo Motomeru no wa Machigatteiru Darou ka IV.