The world has different power system as the Apocalypse hit the world suddenly:

Evolvers: people with special abilities that gives them an edge over the others. For example: some people can have ice control while some people can have other things amongst many.

Evolvers also have grades on their abilities that go from D to SSS.

D level evolver will have shitty abilities that don't help much.

While SSS level abilities will be over the top and immensely powerful.

Tiers are the amount of evolutions an individual has gone through or just to be able to measure the said person's power:

Tier 0: normal human

Tier 1: 3 times as strong as normal humans.

Tier 2: 10 times as strong as Normal humans.

Tier 3: Building level individual.

Tier 4: District level individual.

Tier 5: City block level Individual.

Tier 6: City Level Individual.

Tier 7: Mountain level Individual.

Tier 8: County level Individual.

Tier 9: Country level Individual.

Tier 10: Multiple Contries level individual.

Tier 11: Continent level Individual.

Tier 12: Half world level Individual or multiple                continents level individual.

Tier 13: World Level Individual.

The lifespan of an individual starts to get longer by 100 years with each consecutive tier, starting from tier 4 which is 100 then so on and so forth. You van also maintain your youth longer than a normal human by many times.

Starting from Tier 8, fighters have to comprehend an element to advance further on the road of evolution. 

Evolvers are strong but they have to face more difficulty in advancing as well. They have to comprehend what they unlock as an ability further to keep evolving or they stop on their current level. 

After Tier 10, even comprehension is not enough as they need Heavenly treasures or power sources to expand and evolve.