The Crystal Trade option lets you use crystals to purchase rare 3-5 star heroes, as well as rare crafting materials, which can be accessed via the item button at the top right.
The heroes at the top row can be purchased right away using crystals.
The heroes in the bottom row of the Trade Items window are locked and can only be unlocked if you already own the same card with the same star level. The hero level does not need to match. These particular cards are intended to be purchased so you can fuse them to your duplicate card to achieve a Limit Break.
All heroes available for purchase in the Crystal Trade are refreshed every day.
The crafting materials available for purchase in the Item Window include:
Main article: Fragment Trade
The Fragment Trade option allows you to gain rare and high level heroes once you have collected the requisite number of fragments for a specific hero. The heroes available for trade also include 5-star Evolution Materials.
Hero fragments can be acquired through a variety of avenues, such as the Airship Merchant, the Arena Honor Trade, and Challenge Mode.