Thread:ZeroTwo64/@comment-33201952-20181013193250/@comment-31835132-20181013205331

No problem. When a magical girl uses her magic, her soul gem taints a little (it depends on how much power she uses). When her soul gem taints completely, the magical girl turned into a witch (before Madoka rewrote the multiverse) or disappears (after Madoka rewrote the multiverse). In order to clean her soul gem, a magical hirl has to defeat a witch and take the grief seed she drops.