Unit Enhancing/Evolving

Taken from the game's help section.

Evolving Units
Evolution is the act of combining identical 3★ or higher units to create an even more powerful version of that unit. As with enhancing, evolution requires a base unit, a feeder unit, and gimmel to complete.


 * Regardless of what level your unit is when you evolve them, their final stats will remain the same.
 * The experience and loyalty of both individual units will be combined during the process.
 * Any additional stats unlocked during Limit Breaks will only remain on the base units. Stats present on the feeder card will NOT carry over during the process.
 * For information about Loyalty, please check the section entitled Limit Breaks and Loyalty in the section listed below.