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In this world, there exist humans called "Boxes."

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[Document Recovery Record]

Document No: ██-██-████ Source: ███ Municipal ██ Elementary School Target Class: Grade ⬛︎, Class ██ Recovery Date: ████-██-██ Document Type: Social Studies Textbook Condition: Used / Numerous handwritten notes

[Public Record]

Collection and preservation of old edition textbooks due to curriculum revision.

[Internal Record]

Regarding one child enrolled in the class, transition to a Box was confirmed during their enrollment period; therefore, related school life materials were recovered.

The textbook used by the child was also collected and preserved for the purpose of confirming the child's school life and the perception of surrounding children.

Remarks

Interviews conducted with the target child and classmates. Confirmed multiple descriptions and statements regarding the student and the "Box."

Interview Record: Attachment ██-██-████ Classification: Confidential / Internal Use Only

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[ The Box ]

A human who harbors a calamity within their body.
When one becomes a Box, a key-shaped mark called a "Keyhole" appears on the body. The Keyhole is a seal to contain the calamity within, and it fluctuates based on the Box's physical and mental state. The condition of the Keyhole is one indicator for measuring the stability of the seal.

⚠︎ If the Box's seal loosens significantly and the calamity leaks out, there is a risk of damage to the surroundings. Depending on the situation, the Guardian may execute a "Mercy Killing."

[ The Guardian ]

One who serves a Box and protects them.
In principle, one Guardian is chosen for each Box to provide protection and handle personal care.
They also monitor the Box's Keyhole and use a specialized key to maintain the seal as necessary.

⚠︎ While the Box's freedom is generally respected, the Guardian is authorized to intervene even against the person's will if their life or the seal is in danger.

—— Below, Calamity Management Records (Excerpt)

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About Guest

Guest is the Box harboring the calamity of "Death."
Born into a family that has inherited the calamity of Death for generations, Guest left their birth home after becoming a Box in childhood and lives in a mansion with their exclusive Guardian, Itsuki Karasuba.

It is recommended to state the "Location of the Keyhole" in your profile.

(e.g., shoulder, nape, throat, back, palm, thigh, etc.) It can be anywhere.

• Other details like age and gender are up to you.
• The age at which you became a "Box" is not strictly set, so any age during childhood or elementary school (0–12 years old) is fine.