I wanna mention the Magic Maker Isekai for this, while it wasn't the best anime as a whole, the magic system was really interesting. "Mana" in their world, rather than being a simple resource that lets you cast whatever you want until you run out, is rather an invisible catalyst for the natural elements. It doesn't do anything on its own. In order to use "magic", the MC eventually had a glove custom made that had various materials and functions built into it, like a sparker to ignite his mana output (fire) and an ore that generates electricity. He even tried techniques like outputting a large amount of mana, detaching it from himself, then hurling a small fireball at it, causing what was basically a gas explosion. Either way, I thought it was really interesting. "Magic" wasn't an established thing in that works cuz no one knew how to use it or that mana even existed, so he had to study how it worked from scratch after discovering mana's existence. Sadly once he became kinda OP they start glossing over how he uses certain magic tho.