After going through various other stages in earlier episodes, Sera shows off her true angel form in S2E5.
Triggers: serafullangelform, 1girl, white/purple feathers
You can add breasts, and when you do, shiny skin as well. Beak in the positives and arms,legs in the negatives can help. The purple feathers are seen in the show itself, while white feathers are usually used in fanart.
If illustrious generates the wrong number of eyes, just keep trying new seeds or change steps etc.