FF6: Casting from HP - Bloodmage?

For a skill to do it, would just be a matter of writing the skill to do dmg to caster every time. I'm talking subtract the mana cost of any spell, from HP.

Would just about require a whole new routine during magic casting:

Is Blood Mage?
If so, branch to BM subroutine
If not, continue

Then figure up magic cost of spell,
sufficent mp?
If not, add % to dmg
subtract cost from hp
return

Least that's what I'd see being needed. With something like that, if the caster had mp, it would be normal. No MP would result in stronger magic, at the cost of health. At that point its a question of worth it or not.