In who needs magic anyway or WNMA for short, I have a different take on mana. Mana is part of the blood along with plasma and stuff, and the more one uses magic the more blood is drained, leading to fatigue,weakness,pale skin,etc. "Defects" like our MC have mana in their blood but is inactive and can't be used. Spoiler our MC has the air element but his mana is inactive so he can not use air magic. Since mana comes from blood, there is no such things as mana potions, there is no way around this so magic is used rather sparingly during combat.

In WNMA, I have a unorthodox way when it comes to runsesmithing. Runes are another way to active one's mana but need blood to do so. For example if someone wanted to make a rune that uses fire magic, they need the blood of a fire attuned person and so on. Defect's blood can be used as well but is only half as effective meaning you need twice as more than a normal magic user. The more complex the rune the more blood is needed. Yes runes can be used on weapons but usually not used, as runesmithing is complex to begin with and magic users can do way more with their element than a rune can. Runes are weightless as well. Runes are usually used as elemental barriers and the such. Only advanced magic users understand elemental affinity and might use different runes with different elements.