The ability to get back used ascention items like darts, hidden blades, etc... at the cost of losing the hero you are retrieving them from

Ideas & Feature Requests
1

So if you have a fully ascended 4*. If you decide it would be better that the items used to ascend them would be more beneficial on a 5*. You can get back everything used to ascend the 4*, but in doing so you will lose that 4.