How do Soul Gems get corrupted over time in Madoka Magica?


After seeing how Madoka instantly transformed into her witch form after
killing Walpurgisnacht in one shot in the 4th timeline, it makes me wondering:
**How do Soul Gems become corrupted?**

I assumed that over time the magical girls would lose hope and fall into
despair, which then clouded their Soul Gems. However, Madoka instantly turned
into a witch, without any real reason to despair.




Soul Gems do indeed gradually darken over time, even if a magical girl doesn't
do anything magical. I'd imagine this is because the gem still needs to
magically sustain her body, or something like that. But they also darken for
other reasons - the emotion of despair causes a Soul Gem to darken, and so
does the use of magical powers.

In the 4th timeline, after defeating the Walpurgisnacht, Madoka had no reason
to despair... but she _did_ expend an enormous amount of energy to defeat the
Walpurgisnacht in one shot. Apparently, that was enough to cause her Soul Gem
to blacken completely, thus resulting in her becoming Kriemhild Gretchen.




Soul Gems do indeed gradually darken over time, even if a magical girl doesn't
do anything magical. I'd imagine this is because the gem still needs to
magically sustain her body, or something like that. But they also darken for
other reasons - the emotion of despair causes a Soul Gem to darken, and so
does the use of magical powers.

In the 4th timeline, after defeating the Walpurgisnacht, Madoka had no reason
to despair... but she _did_ expend an enormous amount of energy to defeat the
Walpurgisnacht in one shot. Apparently, that was enough to cause her Soul Gem
to blacken completely, thus resulting in her becoming Kriemhild Gretchen.

