Hero Feather

"Personally, I hold the notion that Hero Feathers are something akin to a Hero’s desire to improve—hopes for the future made manifest."

- Alfonse, Learn with Sharena!

Description and Usage
Hero Feathers are used to Unlock Potential (under Allies → Advanced Growth). This will advance a unit by one star, resetting them to level 1 in the process. The amount of feathers needed to unlock a hero's potential depends on their amount of stars: Prior to the 2.9.0 update, units must be at least level 20 in order to upgrade. As of now, units at any level can be upgraded. Badges is also required to Unlock Potential.
 * to =20 Hero Feathers
 * to =200 Hero Feathers
 * to =2,000 Hero Feathers
 * to =20,000 Hero Feathers

The number of feathers required to Unlock Potential decreases when a unit is merged. The number of saved feathers is equal to the number of feathers that would have been obtained if the fodder unit was sent home.

Availability
Feathers can be earned by playing in the Arena, which grants feathers weekly based on rating and scores.

Feathers are also available as a Daily Log-In Bonus on Mondays and Thursdays, and are obtainable through Quests, Voting Gauntlets, and various other events, as well as 10,000 being available through My Nintendo Points.

Hero Merit is gained on a per-hero basis, once any specific hero reaches 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, or 6000 HM, they will award the player with 500 feathers on the home screen.

Another way to obtain feathers is by Sending Home units, permanently removing them from the player's roster. The amount of feathers obtained by sending a unit home depends on their amount of stars:

The number of feathers obtained by sending home merged units is equivalent to the number if all merged units were sent home as well. For example, a +3 unit would be sent home for 4,000 feathers.