Arks are special sets of gear that grant bonus attributes and stats to your units. They can only have one equipped at a time, and spend soul energy when deployed into a stage.

The stats boosts and attributes are good, but the most important part of Arks are the skills that they grant you. An Ark can have up to six skills, and when a unit wins a battle with the Ark equipped, they will gain Ark Skill Points (AP) for the unlocked skills.

When a unit gains enough AP to master a skill, they permanently learn the skill and have access to it even when they do not have the Ark equipped. Each skill has a different AP rate, which means that they learn at different rates.

To learn all of the skills an Ark can offer, you must first level up the Ark. As mentioned before, you need a large amount of souls to level up an Ark. Leveling up Arks increases the amount of bonus stats, but it also increases the cost of taking the Ark with you into battle.

When a unit has learned all they can on an Ark, it is best to move that Ark to another unit so that they can start mastering the skills on it.