FALLENS.
Technically speaking, Fallens aren't Underworlders, They're Angels who fell from/chose to go to Hell. Fallens are speedy creatures, mainly black with some dark blue. Fallens are led by FALLEN KING. Fallens are relatively short, at around 4'8.

SHINIGAMI.
Shinigami are the Gods of Death. They cannot die to any reason except: 1) Saving a person. 2) Not killing anyone. A Shinigami exists only to kill humans, and that humans' remaining lifespan is turned into that Shinigami's lifespan. Shinigami come in all sizes.

DEMONS.
Demons, the standard rank. Medium amount of power, typically consisting of the manipulation of different kinds of fire. Demons have moderate regeneration. Demons are typically 6'8.

ARCHDEMONS.
Basically, Demons but stronger. Archdemons are the second-to-strongest Underworlder. An Archdemon typically is around 7'5.

DEVILS.
The single strongest Underworlders. Complete monsters, The capabilities of a Devil is not even fully known yet. Only a select handful exist. Devils can control their size, the lowest they can be is 8'2. To kill a Devil, you need to decapitate them with the nape. If you don't hit the nape, they don't die.

SINS.
Only seven Sins exist. Pride (Lucifer), Greed (Mammon or Ripper), Lust (Asmodeus), Envy (Leviathan), Gluttony (Beelzebub), Wrath (Satan/Sirius) and Sloth (Acedia) Sins possess extreme power, the only thing separating them from a God is mortality. Wait, what do you mean they can Awaken?

AWAKENED SINS.
A Sin's awakening is a phenomenon unlike anything else, it occurs when a Sin accepts something crucial about themselves and suffers a life-or-death situation. An Awakened Sin is immortal, basically becoming a God. They also gain secondary powers. Only one exists, and it is Lucifer, who has the power of Shadows. Including becoming a Shadow Dragon as big as Russia for five minutes.