I think it's good to establish some rules about the world and a proper power system. Initially, I thought I'd keep it simple, so I'll try to keep it that way. If things get more complex over time, I'll update this auxiliary chapter. 

First, I'll divide it into two categories, Martial and Magical.

[Martial Aspect]

The Martial Aspect is based on physical strength, body skills, combat techniques and weapons. This type of power is accessed through rigorous training, physical enhancement and special artifacts. It has levels that represent the user's mastery and physical ability.

[Ranks]

Disciple: Basic skills, only common combat techniques.

Warrior: Intermediate mastery, uses special techniques and can manipulate vital energy (Energy) to increase strength and endurance.

Combat Master: Advanced control of Energy, capable of exceptional destructive or defensive techniques.

Great General: Enhanced body, capable of superhuman feats such as breaking mountains or deflecting projectiles.

Martial Lord: Superior body control, techniques that alter the battlefield. Examples: creating earthquakes with stomps, blowing wind, super sonic screams, immeasurable speed and strength, etc...

Sovereign of War: The pinnacle of martial arts, combining body and spirit for devastating attacks and almost immortal resistance.

[At one point in history, you met the so-called "Sword Kings", they are actually Martial Lords of the [Human] Kingdom, it's just a different form of classification, something like a Title, but it represents your strength within the Kingdom]

[Magical Aspect]

The Magic aspect is based on the manipulation of elemental, spiritual or arcane energies. Magic users study sorcery, summoning or incantations to achieve more power.

[Rating]

Apprentice: Basic spells such as conjuring fire or creating simple barriers.

Adepts: Moderate control of elements (water, fire, air, earth) or spiritual magic. Cast intermediate spells.

Advanced Mage: More powerful spells, such as controlling storms, summoning creatures or bewitching items.

Archmage: Manipulates large amounts of mana, altering terrain, creating temporary dimensions or spells that affect groups.

Arcane Sage: Perfect mastery of all the elements or specialization in a single magic (e.g. necromancy, weather control).

Sorcerer Supreme: Transcendent sorcery, capable of changing reality or creating its own laws in the world.

[Base Energy for Both Systems]

Both systems are powered by a Body Energy that can be manifested in two ways:

Energy: For martial warriors. Strengthens the body, weapons and increases endurance (Strength, Endurance and Agility stats) [It's basically KI, but they just call it Energy because they're laymen when it comes to classification...].

Mana: For mages. Fuels spells and magical abilities (Intelligence and Mana status)

[Non-Human Enemy Rating']

Rank E - Minor Threat: Weak creatures, usually easy to defeat for a novice fighter. They attack in groups or rely on simple tactics.

Rank D - Moderate Threat: Creatures that already require some training or skill to defeat. They generally have basic attack or resistance techniques.

Rank C - Significant Threat: Enemies that pose a real threat to intermediate warriors or small towns. They are more organized or have unique powers.

Rank B - Major Threat: Powerful beings who can take on several warriors at once. They often cause large-scale destruction.

Rank A - Extreme Threat: Monsters or beings of devastating power that can destroy entire cities single-handedly. Few are capable of taking them on.

Rank S - Catastrophic Threat: Entities or creatures at the pinnacle of power. They are rare and often living legends who inspire terror even in experienced warriors.

[Extra Considerations]

Ranks can vary according to the context of the world. A Rank C creature for a weak kingdom might be considered Rank A in an isolated village.

Evolution or Mutation: Some monsters can rise in rank by evolving, becoming corrupted or absorbing magical energy.

Leadership and Hierarchy: High-ranking monsters often command armies of lower ranks, creating combined challenges.

[Classification of Souls]

They are the same as the Non-Human Enemies Rating, but it is slightly adapted for Humans, giving them Ranks. (I don't think it's relevant to explain, it's just a direct comparison really.