Apparitions

Spirits
Spirits cannot be touched physically, and are similar to fairies. They aren't leftover from the deceased, but rather represent a force or concept.. Spirits are faceless and have no personality. Though, there are two major exceptions to this rule:

Divine Spirits

Vengeful Spirits have much more sapience and are born from regrets or other strong negative emotions leftover when a person dies or when a disaster occurs. They are among one of the most dangerous beings in Gensekai and Shrine Maidens are tasked with exterminating them if they cause trouble.

Ghosts
Ghosts can only come from humans. Ghosts are born from the souls of humans with a strong emotional attachment to a high degree to a certain place or object. They are not able to pass through objects and have physical bodies. It can be almost impossible to tell when you're interacting with a ghost as they look perfectly human and are warm to the touch.

The best way to help a ghost move on is to show them that they are dead; as they may be unaware of their situation. Providing closure usually makes them continue forward to the afterlife.

Phantoms
This is the being that most closely follows the tradition definition of Ghost. Phantoms are the 'standard' ghostly being and are the souls of someone who has passed onto the Netherworld. They lose their conscious self and have an appearance similar to wisps, however some of then can maintain humanoid forms. They can exist in both the spiritual and physical worlds. Under odd circumstances, Phantoms can be born from even inanimate objects.

Half-human-Half-phantoms can be born in the Netherworld, and have two bodies. A human body which is colder than the average human and a spirit body which manifests as an ethereal wisp that floats around the human body, which is warmer than the average ghost. These hybrids exist in a state between life and death.