Inside Heroes of the Fire EmblemYou probably won’t use this option very often (because of the cost), but it’s worth knowing about.
unlock the potential
You can choose the potential unlock option to increase a character’s star rating once they reach level 20. This will reset that character’s level to one, but will make additional skills available to learn.
Unlocking the potential requires different items depending on the star level you have. Characters with a rating of one to three can level up with Hero Feathers (easier to earn if you do exceptionally well in arena battles) and Badges (your reward for clearing tower levels). To level up a character from four to five, you’ll need even more Hero Feathers, as well as awesome badges (which are also earned by clearing Training Tower stages, but only on higher difficulties). Because of the costs involved, you should think carefully before unlocking a character’s potential.
The Merge Allies option does exactly what its name suggests, and the resulting character gains additional SP and stats in the process.
In order to merge, you must have two allies with the same star rating or better, and they must also have the same name and title. Think of it as a way to get something out of all those duplicate characters you might summon.
However, you should not fuse if you want to unlock a character’s potential, as stat boosts will wear off at that point. You’re better off waiting until your character is rated five stars before merging, so all the perks stay forever.
Source : polygon.com