There are six ranks when it came to Demon Hearts.
A Flickering Heart which Lesser Demons possess.
A Burning Heart which Fiends or Awakened Demons possess.
An Infernal Heart which Archfiends possess.
A Forged Heart which Greater Demons possess.
An Abyssal Heart which Demon Lords possess.
And a Cataclysm Heart which Demon Kings possess.
Each Demon Heart rank also had four sub-grades.
Minor Grade. Prime Grade. Superior Grade. Supreme Grade.
For a demon with a Flickering Heart to advance from Minor Grade to Prime Grade, all they needed to do is to increase the size and intensity of their chaos flame by consuming other demon hearts, battle, and cultivation.
For Lesser Demons with a Flickering Heart, knowing what sub-grade they were in was easy.
Once the size of a Lesser Demon's chaos flame is 25% larger than its birth size, the demon is still a Minor Lesser Demon.
