The Kotoribako (子取り箱, Kotoribako?) is a cursed item found by Satsuki Uruma and was supposed to be locked-away by DS Lab because of how dangerous the item is, until it appeared again in File 8: Little Bird in a Box and attacked Sorawo and Toriko.
The Korobako is a square, woodwork cube, about twenty centimeters to a side. There was no lid, and was assembled from small parts, like a wooden mosaic. Complex seams crawled across the surface of it. The box is wrapped in a powerful silver halo.
After reading a page in Satsuki's notes, a phantom of Satsuki showed up and only Sorawo can see. She holds the kotoribako in her hand and left it with them before disappearing. A red chubby bird with a short beak, resembling a shrike, came out of the Kotoribako and started attacking them. Thinking that it's target was Kozakura, Sorawo leaped to push her out of the red bird's way. It turns out that the red bird is aiming for Toriko.
Migiwa explained that the box is one of the UBL artifacts that Satsuki collected in a secluded mountains and was firmly under lock and key in their warehouse. It was a curse item that selectively causes injury to the internal organs of nearby women and children.
They tried to destroy the box, but only ended up stirring the bird's nest and causing more injury to Toriko. After the birds attacked Sorawo as well, she realized the danger they're dealing it and asked Migiwa and Kozakura to leave the room so she and Sorawo can deal with the Kotoribako. Seeing that the cursed item is like a puzzle, Sorawo and Toriko began their attempt to solve it despite the pain. Eventually the movements they've had to do to solve the puzzle became complex, and the Kotoribako already lost its former shape, becoming a bizarre miniature 3D maze. In the middle of pile of the puzzle parts, is an old dirty cubic box. Silver light that had filled the area around us was emanating from the gaps. When Sorawo opened the lid, the Kotoribako ceased to be.
The story of the Kotoribako first appeared in one of the story threads found in “Shinu Hodo Share ni Naranai Kowai Hanashi wo Atsumete Minai?” (Do You Want to Gather Ridiculously Scary Stories?). A large number of horror stories involving cursed boxes were written on the internet by multiple authors shortly afterwards. The trend “I know a similar story” that is also visible with the Kunekune and The Space-Time Man was in play with the story of the Kotoribako. The story begins when a friend who visits the narrator’s house brings an old wooden box she says she found in a shed. When another friend who has a strong sense for the supernatural sees it, he goes pale, runs to the toilet in fear and calls his father, who is a Shinto priest. He started crying, saying to his father that he doesn't think he could do it and inside his friend is a triangle the shape of a shippou. Since he was the only one who could do it, the friend performs an exorcising, cleansing his friend with the shippou and chanted an incantation to the Kotoribako.
When things settled down, The narrator asks what the box is about, and the friend explains that the box is a Kotoribako, created to exterminate the bloodline of its target. The box only affects children and women of child-bearing age. Inside that box is hatred itself, but there were also a few things in there like fingertips and umbilical cords. He had told the narrator that when the box appears, it was usually his grandfather who deals with it so he was scared to death when he realized he have to deal with it.
- Kotoribako kowabana.net