Woah, what a bump in interest. Since a lot of you are requesting the info via PM, I might as well just post it here so I won't send too many PMs (my PM inbox is already full as it is. xD)
Important Information
▶ Living World ◀
This reality is where all Livings (or humans as they call themselves) reside in, and it is basically our real world. It is a lower tier Reality, meaning that it is unable to fully interact with other Realities unless with the help of a Pact or something else equal to that power. Beings from other Realities can only interact with the Living World if they are Spirits or fully sentient Demons.
*
✵ Spiritual World ✵
This reality is where all Spirits of Deceased Livings reside in, and it usually is referred by the unaware Livings to be their "afterlife." A normal Spirit gradually loses their memories as a Living as they continue exist for a long period of time after their Living's death. An Elder Spirit, which is a Spirit sentient enough to make Pacts with Livings, has the choice to either lose their memories as soon as becoming an Elder Spirit, or to be left their memories from their past life as a Living. Once a pact is strong enough, a Living Pact Bearer is able to transverse into the Spiritual World. There are two versions of the Spiritual World: the first variation is layered over the Living World, where many Spirits that have "unfinished business" are stuck and if left there for too long, the chances of becoming a Demon is high. The second variation is it's own Reality that can observe the other Realities.
*
† Under World †
This reality is where all corpses of Deceased Livings and possibly Demons reside in. After a Deceased Living is properly laid to rest, it's corpse is replicated into the Under World. Due to the recent uprisings of the Demons, where they want to freely roam through different Realities like Spirits, the corpses are prone to become Shadow Replicas under the control of Demons.
A Spiritual Pact is where a Living and an Elder Spirit intertwined their energies together, allowing the Elder Spirit to have unlimited access into the Living World and the Living the power of the Elder Spirit's affinity. Besides the affinity's power being granted to the Living, the Living is also later granted the power to enter the Spiritual World and possibly the Under World. When a Pact is formed, the Living of the pact is given a "Spirit Relic," which is the key to using their pact's power and the very thing that holds their soul. If it is to break, then the Living's soul is released and will cause he/she to instantly die. Fortunately, the Relic is shrouded with a cloaking aura that prevents Demons and Shadow Replicas from detecting the Spirit Relic of a Pact Bearer.
The Spirit that accompanies a Living Pact Bearer is only to be seen and heard by their Pact Bearer or other Pact Bearers, leaving the Spirit completely invisible and unnoticed by average Living society. Spirits are able to fuse with their Pact Bearer to assist their abilities, hear the thoughts of their linked Living Pact Bearer, phasing through solid objects in the Living World, and slightly influence the minds of other Livings nearest to him/her.
There are two types of Demons. The first type is the non-sentient Demon, where it has no humanity what-so-ever and for that, it has a more inhuman and animal-like appearance. the second type is the sentient Demon, having the exact resemblance of a real Living and can create Shadow Replicas, and as well as having some sort of secondary ability related to the mind. The sentient Demons shown in this roleplay are grouped together to be Death Keepers, the threat that the Pact Bearers must destroy.