Sebastian's past is dark and deep, it seems. And Xaneth doesn't like that.
Also woah I almost forgot it was 2013 when updating this. Happy 2013 everybody!
When designing Alyssa's outfit, I wanted to make sure it wasn't redundantly revealing, but rather keep it androgynous or even more masculine than Sebastian's old duds. And so to compliment and contrast that, Sebastian's new getup is more on the feminine side.
Also, Alastor's face.