Tobi Otogiri is a quiet second-year junior high school student who keeps to himself, spending his days having secret conversations with a worn backpack named Baku. The backpack is no ordinary accessory; it was left behind by a strange One-Eyed Man on the day Tobi was separated from his older brother, and it has been his only companion ever since. His unusual routine is disrupted when a classmate, Ryuko Shiratama, suddenly addresses him, saying, You talk to that bag a lot, dont you, Tobi-kun. To his shock, Ryuko can not only hear Baku's voice but also see the bizarre, non-human entities that Tobi has been able to perceive for as long as he can remember.

As the two form an uneasy alliance over their shared secret, strange accidents begin to plague their school. They soon discover that these incidents are the work of these invisible creatures, which are more than just hallucinations. They are zingai, beings that exist in the blurred space between human and non-human, and confronting them forces Tobi to engage with a reality he has been trying to ignore. The story follows Tobi as he is pulled out of his isolated shell and into an adventure where the line between the ordinary and the extraordinary collapses, centering on a core theme of life eating life.

After the initial incidents involving the zingai appear to be settling, a brash transfer student arrives at Tobi's school. She seems to already know about Tobi, Ryuko, and another classmate named Haizaki, and her arrival hints at a larger, hidden agenda. Simultaneously, a mysterious figure known only as S waits for a character named Shizukudani in the nurses office, suggesting that the strange events are far from over and that forces behind the scenes are beginning to move.