User blog comment:TheNewProtagonist/Let's talk about McGon- I mean Goodwitch! Glinda Goodwitch!/@comment-15108745-20130820005428/@comment-11188061-20130820013512

The pointy little arrows you're wondering about behind her cape are a number of devil's tails. I thought it was obvious; shows up a lot in mangas, animes and even visual novels. Even the purple/black coloring was an indicator.

So she's either descendant from a devil's tribe or won against the owner of the cape and now wears it as a trophy or remembrance.