I just wanted to say some things
First, his HP bar. I removed it because I thought it wasn't necessary to have. I plan to delve deeper into that in the far future.
Second, the limit of bullets and blood vials, and other items in general. That was also a mechanic that doesn't apply very well to reality. So I also removed it.
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As to how skills work, this is my idea.
You can skip this info since I wanted to slowly build it in the story.
Although it wasn't shown, skills have rarities. This can be interpreted as "ranks"
This rank and rarity are based on a series of parameters too numerous for me to list.
So just remember that.
This rarity is also based on your Class. A swordsman skill may be better in a swordsmanship class instead of a spearman class.
Usually, the lower the rank and rarity of a skill, the higher the number of levels it will have.
The higher the number of levels, the higher the chance the skill will automatically evolve once it reaches max level.
But once again, this is subjected to your class and the origin of the skill itself. It may very well have 90 level and not evolve. Or it may have 90 levels and be of a higher rank than a skill with only 20 levels
Skills tend to be harder to level up as you rank than up. using the previous example, the skill with 90 levels would be harder to level up than the one with 20 because it has a higher rank.
once a skill evolves for whatever reason, it will restart at level 0 with a lower level cap. This process will repeat until the person isn't capable of evolving the skill any further or the skill simply evolves into a form that doesn't have any levels.
There is an extra factor. A maxed skill with 30 Levels may not be able to evolve at all. And that's because of its lower potential. It may be incomplete or require a special circumstance to be achieved before evolution.
To go beyond that... There are many ways. The simpler is to fuse another skill into another, changing it.
This is also one of the riskier ways as it may completely destroy the skill by changing it into something you don't desire.
The other ways consist of pushing the skill to its limits or achieving some sort of condition. There may be more...
I plan to add more info in here in the future.