Link to the thread in the LoL forum:
https://boards.na.leagueoflegends.com/en/c/skin-champion-concepts/EAFPhJY9-skin-idea-dark-star-xerath

Xerath craves power even if it destroys his own body.
The Dark Star skins are about the dark cosmic powers like black holes, rifts, etc.
The two go so well together, I am surprised it hasnt been done yet.

The development for this skin took quite a while. I had a bunch of ideas I wanted to explore and some that were very interesting but didnt quite work (like the cross armed or the red one). In the final version I exchanged the inner glowing lines with a more obsucre glowing structure that's inspired by galactic clouds/nebulae. If this were to be animated, I'd imagine the cloudy core to slowly rotate.
The glow on the collar could have a subtle animation to make it radiate away from the core.