@cherokeemoon I understand what is going on, but the terms and the way everything is said is confusing. I think this was just translated (i don't want to say poorly, but it could have been done better) I think it would be better if the translation team just seperated the two types by calling them [Heal] and [Regen]
The other girl's magic does heal. Its just a form of regeneration (thus [Regen]) . It allows the injured to quickly regenerate their body at the cost of the bodies own energy. (most likely it uses the bodies own calories, fat ect...) I only say that because of the science like insight this series seems to want to pursue. But from the wording, it sounds like it uses the persons soul energy (maybe their mana?) Its like when a lizard loses its tail, it needs to eat alot to get the mater/energy to regrow that tail. The boy in this case lost several limbs, and they regrew because of [Regen], but it took the energy from him directly, energy that was sustaining his body (which is why he looked emaciated) He was probably dying from like organ failure or something.
anyway, [Heal] what the MC uses, uses the mana in air to heal a person. And not the persons own energy.
Its probably going to be discovered later by the MC that anyone who uses [Regen] should eat alot to offset the cost or something.
Deeper dive... Rethinking everything, since people died a few years later after using [Regen] and the boy began dying just days later (given he had super serious injuries) Maybe Regen uses ones own mana to heal HP, but if the injury is too severe and the persons own mana is not enough, it suppliments the energy needed by using that person own lifespan or life energy. As if each injury was a "Debuff" that was being cured with HP since the MP was all used up. Its Blood Magic! restoring mana by sacrificing HP!