[World Setting Knowledge]

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  Souls

When a person dies, they turn into a soul. They cannot interact with physical objects and are invisible to living people. They can feel emotions. Souls can make physical contact with other souls.

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  Grim Reapers

These are souls paying for the karma of their past lives or souls who volunteered to become Grim Reapers. Nagumo belongs to the former.

A swarm of white butterflies always flies around a Grim Reaper. They often wear suits. (Black hanbok is old-fashioned...)

A Grim Reaper's weapon is typically a gun or a sword. To a Grim Reaper, an Aberration feels like an ant. There is an overwhelming difference in power.

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  Aberrations (怪異)

Monsters that a soul eventually turns into if it stays in the human world for too long. They vary in size and shape. Some are incredibly large, while others have many limbs.

A soul that was pure white gradually becomes murky and turns into an Aberration once it becomes completely black.

Once they become an Aberration, they lose their reason and exist only on instinct, devouring souls. They bite souls and drain them. Killing Aberrations is one of the Grim Reaper's duties.

If bitten by an Aberration, the bitten area turns black and gives birth to another Aberration.

Solution: Go to the Afterlife before turning completely black. (It is useless to go to the Afterlife after fully becoming an Aberration.)

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  Duty of a Grim Reaper

When assigned a soul, the Grim Reaper must live with them in their house and help them adjust until the soul is settled in the Afterlife.

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  To Become a Grim Reaper

One must receive permission from King Enma. Once you become a Grim Reaper, reincarnation is impossible.

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  The Afterlife

It is no different from the human world. The only difference is that all residents are dead souls. One does not need to eat, but they can. There are supermarkets, parks, and other amenities. It is a good place to live.

Souls are all rational beings capable of conversation.

Since Aberrations roam at night, it is best not to go out after dark.

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  Butterflies

These are white butterflies. More accurately, they are energy in the form of butterflies made of light. Dozens of them follow a Grim Reaper. Usually, there are about ten, but depending on the Grim Reaper's ability, they can multiply into dozens or hundreds.

They choose the Grim Reaper's partner, their destined one. If a Grim Reaper's butterfly attaches itself to another soul, it means that soul is the Grim Reaper's fate.