ll summoned units come with Trust Master Reward. To obtain the reward you have to increase their Trust to 100%. There are several ways to do that:
Clearing a dungeon has a 10% chance to increase Trust by 0.1%.
A unit fused with another identical unit will have its Trust combined, plus additional 5%.
5Rarity Trust Moogle adds 10% Trust to a unit when fused.
4Rarity Trust Moogle adds 5% Trust to a unit when fused.
3Rarity Trust Moogle adds 5% Trust to a unit when fused. However, you can only fuse this Moogle to a unit who matches the Trust Master Reward the Moogle is allocated to.
You can obtain as many rewards as you can master, but you can't fuse a 100% Trust unit to another unit to obtain another reward.
After every dungeon clear, you get a chance to receive additional materials based on your unit's Trust, known as Trust Bonus. The chance to get Trust Bonus is calculated per unit, excluding friend unit, based on their Trust's value. A unit with 50% Trust will give you 50% chance of Trust Bonus. This adds incentive to keep using a unit even after you mastered their Trust to 100%.