The Kaibutsu are white-haired, pale-skinned schoolchildren with bleeding faces, all wearing white school uniforms. Initially .flow's answer to Yume Nikki's Toriningen, the Kaibutsu have become far more than standard enemies over the course of the game's development. Like the Toriningen, the Kaibutsu also come in three varieties.
The Kaibutsu in all their forms appears throughout the game. There are several special ones as well.
- In the Plant Labyrinth, Footprint Path and the Bone Maze, calm Kaibutsu wander around. They will only chase you if you smack them with the Iron Pipe.
- In the Industrial Maze, Isometric Pathway, the Sugar Hole Painting, and the room leading to the Footprint Path there are Kaibutsu that always chase regardless of whether one has been hit or not.
- In the Sugar Hole, a Kaibutsu will occasionally be seen sitting at the bar drinking a beer, and will kill Sabitsuki if she attempts to hit it with the Iron Pipe. (See Bar Kaibutsu.)
- In the pathway to the Corrupted School, three Kaibutsu will chase Sabitsuki if she approaches them, and a fourth will appear to the south and instantly hit her if she isn't invisible.
- In the entrance to the School, two Kaibutsu will be standing behind the counter, and will change the menu upon being interacted with.
- In the hallways of the Corrupted School, a unique type of Kaibutsu is found, these ones carry steel pipes and resemble Sabitsuki. They chase Sabitsuki, getting progressively faster.
- In Rust's version of the Corrupted School, several of the Sabitsuki-lookalike Kaibutsu will turn into giant Red Demons, screaming as they do so. At the basement, Rust will turn into a Sabitsuki-lookalike Kaibutsu, and when interacting with Smile she will kill him with the pipe she holds.
- Kaibutsu translates literally into 'monster'.
- The Kaibutsu were canonically said by lol to be Female.
- The Kaibutsu found in the Bone Maze after the Hospital will become extremely fast when angered. Because its behavior is similar to the Toriningen found in the Candle World in Yume Nikki, this one is sometimes nicknamed the 'Candle World Kaibutsu'. The details of the event can be found here.
- If one hits the test tube Oreko is in in the Industrial Maze, the Kaibutsu will become aggressive and chase Sabitsuki, even if none of them have been hit.
- There is speculation that the Kaibutsu were people Sabitsuki knew either in the hospital or were her classmates during her time in school.
- The Kaibutsu could have been children with a similar disease to Sabitsuki and could have been testing subjects to a cure which ended up with major consequences. The same type of cure could have been used on Sabitsuki with a longer wait till she becomes like them. It is thought this because as during the True Ending Sabitsuki can be heard giggling much like the Kaibutsu before she attacks the Gas Mask Maid.