Asteria's formal attire. She was originally a god who made stained glass in heaven. The beautiful reflections of the glass resembled the light of the stars in the galaxy,
and were praised by the other gods.
Asteria's attire was like that of a nun, as she worked hard for the other gods.
Now that she has left the divine realm, it is only a vestige of that.
The Glass Sisters of the Glass Church are a distorted church with no object of worship or master to serve.
Some humans worship her as a god, but she disapproves of this, as she was originally the one doing the serving.
This is probably why she calls her followers "sisters."