Merge Allies

Merge Allies is a feature that allows you to merge duplicates of the same Hero to gain benefits. It can be found under the Ally Growth menu.

Effects of Merging
There are a few things that can happen when merging depending on the star rarity of the characters used:

The remaining enhanced character will receive the bonuses listed above, but any levels or SP from the source ally will be lost forever.

Additional SP
The amount of SP awarded to the resulting unit after a merge depends on the rarity of the sacrificed unit, as well as the number of merges the sacrifice already had. For merged source units, each additional unit merged into it previously adds the base SP of that rarity again. For example, merging a +2 unit into another unit grants the base SP of 20, and an additional 2 times 20, for a total of 60 SP.

Merge Stat Bonuses
When merging two units of the same rarity, two stats will be selected to be increased by one. The two stats selected for each merge are the two highest level 1 raw stats for the character (after considering Asset and Flaw), which have not yet been increased. This repeats for each successive merge, making all stats increased by a total of 2 points each at +5, and 4 points each at +10.

In the case of a tie between two level 1 stats, the first one in the listed order will be chosen, HP > Atk > Spd > Def > Res.

The fact that HP is the highest Level 1 raw stat (without considering Weapon Mt and stat-increasing passives) for every unit means that HP will be one of the increased stats at +1, +3, +6 and +8.

As of Version 3.2.0, if a unit has an Asset and a Flaw, then its first merge will add an additional 3 or 4 points to its Flaw stat, whichever is enough to negate the Flaw. For units that whose traits are normalized, their three highest level 1 raw stats will each gain 1 additional point upon the first merge.

Example
Consider a hero (neutral 5-star ) with the following raw stats

The first merge would increase the HP and Spd, as these are the highest two raw stats. The second merge would increase the Atk and Res, as these are the next two. The third merge would increase the final stat, in this case Def, and start a second round increasing HP, the highest raw stat. The fourth merge would increase Spd and Atk, and the fifth merge would increase the remaining two: Res and Def. The sixth merge would increase the HP and Spd, as in first one.
 * HP, Spd, and Atk will increase by an additional point each, as the unit is neutral and these are the highest three raw stats.

Merges seven through ten echo the merges two through five.

If this Olwen had an Atk Asset and a Res Flaw, her raw stats would be as follows, introducing ties.

The first merge would increase the HP, as it is the highest stat. To break the tie for second between Atk and Spd, Atk is chosen because it is the first one. The second merge would increase the Spd, and break the tie between Def and Res by choosing Def, as it is the first one. The third merge would increase the final stat, in this case Res, and start a second round increasing HP, the highest raw stat. The fourth merge would increase Atk and Spd, which both tie for highest, and the fifth merge would increase the remaining two: Def and Res. The sixth merge would increase the HP and Atk, as in first one.
 * Res would increase by an additional 3 points, as that is this unit's flaw, and 3 is enough to negate the flaw.

Merges seven through ten echo the merges two through five.

Merged Icon Backgrounds
The Hero's icon background color changes depending on the rarity and amount of merges. Summoner Support overrides the standard background and border, but displays merges as rarity does.

Miscellaneous
Heroes that share the same illustration, name, and epithet are considered the same Hero. Even if the character is the same, Heroes with different illustrations and epithets are considered to be different Heroes. As such, you cannot use them in Merge Allies.

You cannot merge favorited heroes into other heroes. You can tell a unit is favorited if there is a heart icon on the character's icon.

To un-favorite a character, press and hold the character's icon to get into the character's status page. Tap the heart to unfavorite that character.

Units that are +10 can still be merged for additional SP. However, if a unit is both +10 and has 9999 SP, it cannot accept any more merges.

Trivia

 * In the Japanese version of, Merge Allies shares the same Japanese name as the Limit Breaker skill from.