"The spirit Plane" is known as a location of indifference, equality and emotions in the air such as contemptness, confusion, anger, denial and patience.
All of these have in common, that the spirits are troubled by something, stopping them from progressing.
The spirit plane is a dimension above the normal, mobian one. A 5th dimension. Something unperceivable to the common eye, needing some magic or scientific device, in order to read and acknowledge their existance.
There is an unspoken rule in that dimension, only taught by the endlessly resting, unwilling to move on nor accept death; "If you see an angel, talk, if you see a demon, run."
That knowledge is passed onto those, desperately seeking answers and wanting closure.
In the spirit plane, is your first stage after passing; there is a moment, where you see how, where, when and why you died. It's not visible by the naked eye, though you can ask any spirit, as every spirit has the ability to share memories with one another, by a spirit touching ones forehead with their palm. You might find loved ones who waited for you in that plane of afterlife or you might find, you are ready to be trialed and judged, for where you'll be sent to live as a preparation for dependant on religion/belief- reincarnation, next stage of life, etc.
You might be picked up by an angel or a demon, if you feel, you have no purpose, or require help. If fate isn't so sure, you'll be sent to the spirits of justice and ruling, to be trialed and questioned, until a clear alibi and motivation is understood, that a person formed, for all of their actions they'd done, that if need be, questioned.
Demons tend to pull you along with them, without any sort of negotiation or pleas to be reconsidered, which is why their reputation is so terrifying, to most spirits who hid from said demons. Demons tend to take more than a few along with who they're supposed to take, some are soul-eater types, meaning you could end up vanishing entirely or becoming part of the demon.
Angels tend to tenderly inform and take you with them willingly, if you tell them you'd like to wait or stay, they are obligated to let you be by request, unlike demons who are forced under the command, of their deadly-sin family alignment.
If you do agree to go, you'll be transported to the Divine Sanctuary and they will ask a few questions, to determine what type and where you'd most likely prefer to stay. If you have any sort of relative/partner/pet, they will also let you know, of they've been waiting above or if they are still present/have moved on.
The plane is mostly populated around graveyards and century-old housing, memorials or certain statues/locations. Folk will usually share their story, be it excitedly or distraught, some indifferent.
If you're a spirit with no beliefs, you can simply choose to stay in the plane or vanish forever, with no trace or warning. Noone will know of it and you die as a final, last time, forever.
Spirits in this universe can "die a second time" (atleast how one of my friends called it LOL), by being exposed to high mental-stress. Angels and demons tend to be much more resilient, yet spirits are the weakest out there and are easily susceptible to high-stressors, causing them to dissolve back into the air, into dust, then travel back to their graves, or their origin-point such as memorials.