Unlock Potential under the Advance Growth Tab can only be described as ranking up. Essentially what this does is raise the number of stars for the selected hero, 5 being maximum. The amount of resources required to Unlock Potential varies depending on the rank the hero is advancing to.
What You Need To Know
1. Hero must be Lvl. 20 or above to Unlock Potential
2. Resources required include "Hero Feathers" (required for all ranks) and Badges (obtained from Training Tower)
3. Badge required varies depending on the rank your selected hero is advancing to (4 star to 5 star requires Great Badges, obtained from Training Tower 6 and beyond)
4. Hero Feathers can be obtained through PvP, gift from Friend’s visiting heroes (found at the bottom of the home screen) and giving up heroes at the "Send Home" page (Feathers obtained varies depending on hero rank)
5. As mentioned in "Fire Emblem Heroes Guide: Merge Allies" all accumulated + gained will not be carried through
6. Under normal circumstances (no special events) grinding for materials required for raising a 4 star to 5 star could take 1-2 months
7. Hero Lvl. is reset back to 1 upon Unlocking Potential.
Buttons are located in the exact same location for English versions
▲Hero Lvl. resets to 1 upon Unlocking Potential
▲Resource required varies depending on Hero rank
▲Hero Lvl. Does not affect the amount of materials required for Unlocking Potential