Becoming a ghost (亡霊 bōrei) is what happens to humans when they die and are unable to rest in peace. Being dead, one might think that they no longer have any need for food, sleep, physical pain, or other inconveniences of the living condition. Whether any of that is true is currently unknown. What we know is that they like to party, eat, behave cryptically, continue doing the same activities they enjoyed in life, and generally have a good time.
Within the safely guarded borders of the Netherworld, ghosts live out the days of their afterlives pursuing whatever happens to come to mind. There are some vague hints about a chain of command that even the dead must follow, but it doesn't seem like specific details have been worked out. Ghosts are easily distracted.
The downside on being a ghost seems to be not having a real body. In fact, Ghosts seem to be able to drink and eat because they're able to touch objects but they never have a feeling of satisfaction on it. But it still isn't obvious.
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