Units

Taken from the game's help section.

What are Units?
Units are powerful warriors that you will summon to fight for Ishtaria.

There are multiple ways to acquire new units such as through card packs or via events. Feel free to protect your units by setting them as Favorites. This will protect your card from accidental mishaps that may occur when selling or sacrificing units.

Unit Levels
Your unit's level represents how far they've come in terms of strength.

You can give a unit the EXP necessary to level up via the Enhance feature. Units will enjoy stat increases as their levels rise.