A fun little thing I've done to try and make Inkagafar feel unique is to rename mana and have an in universe explanation as to why it exists. Mana is called Caelum Energy (or just Energy) and is an energy source pulled directly from the heavens, but only certain people (either born with the power or trained to manipulate it) can do this. Gameplay wise it's identical to mana in any other game. It's used for all types of spells and is sort of a Deus Ex Machina, capable of doing whatever is necessary (provided that the Energy source is great enough).

The main purpose for this is to ensure that it feels 'realistic' in how it's included in the game, and not just like an afterthought thrown in to excuse certain skills existence. There are certain rules I'm trying to follow with Energy to make sure it's consistent too. Long story short, Energy is mana but with lore. The abbreviation for it is CE, so if I ever mention 'CE costs' I basically mean 'MP costs'.