Interesting filler/side characters

Many people seem to hate filler episodes, being rather pointless in the way that they don't contribute to a main plot. Characters in episodes like these are ones we will probably never see again either, and therefore there may be no emotional attachment to them, or reason to even bother with them.
However, some of these characters are pretty interesting, despite having as much use as a lump of dirt.

- Kakero/Kagero (sp?) from a Naruto episode was one of those characters. I think it was sometime after the 100 episode mark where this multi-part person caught my interest:

Spoiler:

First, we see Kakero as some kind of pugly person that had a gigantic ground vortex attack which just about decimated the nearby house. He disappears for a while after the one ninja girl tends to Naruto.
After that, surprise! Kakero was actually a girl with chakra wings who actually looks anything but pugly. She then uses another devastating attack called "Ephemeral Wings", despite the fact that she dies sometime after using it.

It might be hard since most of the time, filler characters aren't very memorable at all, but do you have any that stick out in your mind?

Jam it back in, in the dark.