Hajime, a young man who left his rural hometown for Tokyo, returns under circumstances that are not immediately explained. He reconnects with his childhood friends, including his boisterous and fiercely protective best friend Kai, whose younger brother Taiyo disappeared near a local cave years ago. The group, now in their early twenties, gathers for a reunion and eventually decides to revisit the so-called "man-eating cave" on Mount Shirao, a place shrouded in local legend. According to the stories, a band of defeated samurai once hid treasure in the cave, and every explorer who entered afterward never returned. The cave is also the site where Taiyo went missing twelve years prior, a tragedy that has haunted the group ever since.

The setting is the claustrophobic, lightless interior of the cave itself, a maze of narrow passages and deeper chambers that becomes a death trap when the entrance collapses shortly after the group enters. Cut off from the outside world with no cell service, limited supplies, and failing phone batteries, the friends quickly descend from nostalgic adventure into a desperate fight for survival. They are not alone. Before the collapse, an occult streamer named Yosumin had been investigating the cave for her channel; the group finds her smartphone and selfie stick, along with a horrifying video recording that reveals the presence of something living in the dark. They soon encounter the cave's inhabitants: pale, grey-skinned, large-eyed humanoid creatures that move through the darkness with unsettling ease. These beings are not mindless beasts but appear to have a rudimentary intelligence and a predatory purpose. The group realizes that the "man-eating" reputation is literal, and that Yosumin was only the latest victim.

The main characters include Hajime, the quiet and somewhat withdrawn protagonist who carries a personal trauma connected to the cave; Kai, the loud, optimistic leader who refuses to believe his brother is dead and tries to keep everyone's spirits up; Riku, a pragmatic friend who explains the cave's history; Akane, a female friend who becomes an early source of unease after exhibiting strange behavior; and Minamoto, another member of the group who is targeted while trying to sleep. As the survivors move deeper into the cave, tensions rise, and the psychological strain of the isolation, darkness, and constant threat of attack begins to erode their rationality and trust in one another.

Notable narrative arcs include the discovery of a collection of children's belongings deep in the cave, including Taiyo's shirt, which deepens the mystery of what happened to the missing children over the years. The story also explores Hajime's unspoken past, the reason he left for Tokyo, and the painful memory of Taiyo's disappearance. The creatures themselves are a focal point of the horror: they are not simply monsters but are strongly implied to be the transformed remains of the children who were taken by the cave over generations. This raises the central thematic question of whether the cave is guarded by a god that demands sacrifice or a predator that simply consumes. The manga weaves the immediate physical threat with a slow-burn mystery about the cave's true nature, the origin of the creatures, and whether any of the group can escape before they become part of the cave's history themselves. The story is ongoing, with the survivors trapped and the body count rising as the line between the human and the cave-dweller becomes increasingly blurred.