Tiffania's familiar is the one with the power to carry a Void spell and boost it's strength with their lifeforce. You don't have to die in the process unless the spell is ALSO deadly to you, and the stored spell is activated by the familiar's choice(which basically means it can't kill you unless you chose to let it). It's a Familiar of Spell Storing, and Brimir was an asshole to use it that way, it also explains his extreme guilt later, because seriously, you made one of your friends carry a suicide spell, and they were willing to go through with it.
If Tiffania learns Explosion Ryoga could store a nonlethal Explosion to use on Ranma next time
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