I know what a HUGE pain in the arse it is to draw Cala's hair properly.
Drawing the hair wasn't the worst (it's not so hard if you use a reference image - I'm actually not a very skilled anime illustrator). Animating it and then shading it and then properly animating it with the shading... that was a major pain.
What I least like of the image is how I was unable to draw the sort of white highlights that Cala has on her hair. Drawing them frame per frame was out of the question and I had to use some photoshop processes to try to emulate it, but wasn't able. I eventually had to accept using a blurry highlight unlike the sharp ones you see in most viper hairs.
Oh well... Maybe I'll get it right next time