Affinity

Affinity refers to how well the Units get along with each other.
Units that are close and have high Affinity for each other receive a boost to their stats.
As the Affinity Lv. increases, the range and effect of stat boosts also increases.
You can view a unit's affinity with other units and their affinity effects in their status details.

Affinity between units increases when they embark together on the same battle.
Attacking or using Abilities while stat boosts are in effect will increase Affinity EXP.
Conversely, if a unit's HP drops to 0 and they are KO'd while stat boosts are in effect, Affinity EXP will drop.
*If you use a Skip Ticket to complete a Quest, Equipment Proficiency will increase based on the number of clears regardless of how battle plays out.