Terra
This is akin to the universal concept of eternal paradise; people who extended kindness to others, despite the sentiments not always being reciprocated, find themselves here.

Ferro
This is what some might perceive as an upper level purgatory, where to a certain extent, the people who satisfy this existence continue to live their mundane lives. People who find themselves here are those that never committed any heinous crimes, but likewise, often had not felt inclined to commit many kindnesses.

Umbra
This can be perceived as a lower level purgatory, where after entering the Tunnel, the individual finds themselves reincarnated into someone new - essentially provided the opportunity to start over. Typically, the individuals here are those that committed petty crimes throughout their lives, which while not terribly detrimental to others, still caused some grievances.

Tenebris
If Terra signifies eternal paradise, Tenebris signifies eternal damnation. The operation of this station is similar to that of Umbra where the soul is reincarnated into someone new, but unlike that of Umbra, the opportunity to begin life anew is only an illusion. The individual experiences a cycle where they become a new person, commit a murder, and experience the despair all over again for eternity. As the aforementioned sentence indicates, the only way one can find themself on this station is if they commit a murder.