Mortal Mana Core Major Ranks are as follows:
1. G
2. F
3. E
4. D
5. C
6. B
7. A
8. S
9. SS
10. SSS
Each Major rank has 3 levels:
1. Minor(-)
2. Intermediate
3. Peak(+)
When you first awaken, you always start at G-, and each minor rank up gives minor stat boosts all across the board, mana becomes a bit easier to refine and control and things like strength, agility, etc… increase slightly, and for every major rank up, it's not just a massive increase in stats and mana reserves, but your very existence gains more ontological weight, think of it kind of like an evolution, you don't just get 'stronger', you become better looking(improved symmetry and golden ratio alignment), your mind gets sharper, your very soul becomes heavier and denser. But you also won't suddenly go from average to model tier in one major rank up, that isn't how it works, if you are, say, average in looks at rank G, maybe by rank C or B you would be considered handsome/pretty by modern earth standards, it all depends on what your baseline was.
Also, every human at the age of 12 awakens their mana core and becomes rank G-, only exceptional geniuses can awaken earlier, because it's at age 10 that the body starts naturally attuning to mana, and it takes around 24 months for the body to form a mana core from that point. MC and those with SSS+ rank soul potential however typically awaken 1-2 years earlier because their bodies attune to mana faster.
Now Soul Rank Potential, this is the limit of what mana core rank you can reach, yet distinct from 'Talent', someone with high talent but a low soul rank potential is still hard capped.
Soul Rank Potential Major Ranks:
1. G
2. F
3. E
4. D
5. C
6. B
7. A
8. S
9. SS
10. SSS
Each Major Rank has 3 levels:
1. Minor(-)
2. Intermediate
3. Peak(+)
And to be clear, those born with an SSS+ soul potential are extremely extremely rare, almost vanishingly rare, with maybe 10-15 at most per generation, and remember, just because 10-15 appear doesn't mean they will live long enough to grow strong. Also if they are born in bad conditions(like the slums), they may never get noticed. Basically the 'elites' of this world, typically have A to SS rank soul potential, with most important characters having SS(or higher) soul rank potential.
Also it is important to note that soul rank potential cannot be changed, ever, no one can alter the soul itself, besides maybe a god(but they view altering souls as heretical, even gods with authority over souls would never do it, even if they technically could in theory), basically my point is that you can't just eat a magical fruit and suddenly have SSS rank potential from C rank, that's not how it works. There is no artifact or potion that lets you alter your soul potential rank.
Also, mana is everywhere on the planet(except for certain places like demon territories(mentioned in **World, Geopolitics, Races, etc...**), and to rank up(say from G- to G and so on) you need to absorb mana and refine it through your mana core, soul rank potential combined with natural talent dictate how easy and fast this process is.