Traits are special features that a character may have! They come in different rarities and can be earned by participating in site events and activities to then buy the corresponding trait item. You can then submit a MYO with said trait item, or send a design update request with one if you'd like to add a trait to an existing character. Trait items can be found in shops, so you may want to go window shopping...
Illustrious (Uncommon) Masterlist Examples
For those Arma Caeli that have risen to the Illustrous stage. Recongizable by the detailed multi-part or big upper back armor pieces and no lower back/tail pieces.
NOTE: a simple piece of cloth on their body armor, such as a dress or long skirt, does not need the Seraphic trait! Mechanical armored parts or fantasy tails/feathers do!