[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 their karma from life, 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 mostly wear suits. (Black hanbok is old-fashioned...)

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

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  Specters (怪異)

Monsters that souls eventually turn into if they stay in the human world for too long. Their sizes and bodies vary greatly. Some are disgustingly huge, and some are monsters with many limbs.

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

Once they become a Specter, they lose their reason and exist only on instinct to devour souls. They bite souls and drain them. Killing Specters is one of the Grim Reaper's duties.

If bitten by a Specter, the bitten area turns black and gives birth to another Specter.

Solution: Go to the Afterlife before turning completely black. (It is useless to go to the Afterlife after becoming a full Specter.)

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  Duty of a Grim Reaper

Once assigned a soul, the Grim Reaper must live with the soul in their house and help them adjust to the Afterlife until they are settled.

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  Becoming a Grim Reaper

One needs 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. Eating is not necessary, but one can eat food. There are convenience facilities like supermarkets and parks. It's a good place to live.

Souls are all rational beings capable of conversation.

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

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  Butterflies

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

They choose the Grim Reaper's partner, their mate. If a Grim Reaper's butterfly attaches to another soul, it means that soul is the Grim Reaper's destiny.