If that is the case, then they are generating negative karma simply by using magic. Unless magic itself is inherently wrong, which doesn't really jive with the rest of the setting. I think the corruption is more akin to what was happening with Negi, before he gained control of his dark mode. Actually, that works better than I initially thought, as it was stated that if Negi hadn't been able to control himself, he would have become a mindless demon bent on destruction, and would have had to have been put down. Most people don't have what it takes to do what Negi did, and he nearly failed. Plus, I'd imagine the Soul Gems are set up to make it even harder, if not impossible for the girls to catch themselves before they loose themselves.
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Stand between the Silver Crystal and the Golden Sea.
"Youngsters these days just have no appreciation for the magnificence of the legendary cucumber." --Krityan Elder, Tales of Vesperia.
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Stand between the Silver Crystal and the Golden Sea.
"Youngsters these days just have no appreciation for the magnificence of the legendary cucumber." --Krityan Elder, Tales of Vesperia.