Dead Man's Questions

Taking a page from the Jojo's Bizarre Adventure's spinoff, concept ideas and rules for a ghost character who exists in a purgatory-like state but has to accomplish tasks in the living world (possibly integrated into Subssen Canon via a mission from either Soul Society or Enma-Daiou:

The Spirit Agent:

• Can freely enter any space they wish UNLESS it is locked and a living person is in there, in which case they need to be invited in by that person somehow;
• Loses energy if a person or animal touches them. If they lose too much energy they cease to be. However, they can initiate touching no problem, like a poltergeist.
• Can otherwise phase through matter and collect physical items which can then be converted into reishi and back again.
• Can be heard if they speak, but cannot be seen by normal people.
• Can collect and keep "ghost items" too (items that have long since ceased to have physical form).
• Can lose limbs in their ethereal form, but then rebuild them if they have access to enough reishi and a good enough mental visualization of the body part that was lost.

There are creatures called spirit cleansers that can eat them, destroying them permanently.