Evolution is completed in the Recipe Workshop. Certain wardrobe items can be evolved by obtaining a specified quantity of the item and paying a cost in Gold to evolve the item to the next level. Evolving an item will always leave one of the base item in the player's wardrobe. Evolvable wardrobe items may have either one or two evolved stages. Evolution is unlocked after completing stage 3-3 Prime Minister's Secretary (Maiden).
Evolved items are often referred to with the terminology "Rare/Epic" or "Gorgeous/Treasured" (for stage 1 and 2 respectively). However, some items have different names for evolved pieces, for example Phoenix Messenger and its evolution Moonlit Blue Phoenix.
Most commonly, six base items are required to evolve an item to Rare level, then four Rare items are required to evolve the item to Epic, for a total of 21 base items. However, sometimes different quantities are required in order to evolve items. For instance, only three Assassin Faith dresses need to be crafted in order to evolve Assassin Faith-Rare, and a full twelve Spring Harbinger are required to evolve Twilight Phoenix.
Evolvable items can be found as drops in certain Maiden and Princess level stages, randomly drawn through a Mystery House pavilion, purchased through the Association Store or the Clothes Store, crafted, reconstructed, bought through events or obtained by opening the Lost Casket.
For a full list of evolvable items, see the Evolvable category.