Currently only known way to obtain is to roll more than 5 duplicates of a 5★ trainer. From the 6th duplicate and onwards, this item can be received. Can only be used for 5★ Sync Pairs.
5★ Power-Ups obtained from events have a limited time period before they expire and disappear from the inventory! If you don't currently have the sync pair you want to use it on, you can save it until the last day possible, but don't forget about it or it will disappear.