You can feed Fruit to your Limimins.
You can earn Fruit from Login Bonuses, the Expedition Limimin, and Main Quest Treasure Rewards.

Attack Fruit, Defense Fruit, Magic Attack Fruit, and Magic Defense Fruit
Feed the Fruit for the stat you want to increase to your Limimin!
Stats cannot be reverted once they've been raised, so think about your decisions before you feed your Limimin.

Your Limimin will level up once its stats reach a certain level.
Your Limimin's appearance will change at level 5 and level 10.
After level 10, your Limimin will learn a new Ability every 5 levels.
Limimins can know up to 3 different Abilities at a time, and their Abilities can trigger various effects during Quests.

Every time you feed your Limimin a Fruit, its Fullness Gauge will fill by 1.
Once your Limimin is full (when their Fullness Gauge is at 5) they won't be able to eat anymore. They'll get hungry again after some time, so just wait!
The Fullness Gauge empties by 1 every 4 hours. Attempting Quests will decrease the amount of time required for them to get hungry by a little.

*After learning 4 Abilities, you must make your Limimin forget one Ability in order to learn the new one.

*Fullness Gauge reduction time is shortened based on the EXP earned from a Quest divided by 10 (this number is then converted into seconds).

*The time is not shortened by participating in Guild Battles, Colosseum Battles, and EXP Quests.

*The Fullness gauge reduction time is shortened by participating in United Offense and Super United Offense Battles, but your Limimin will not use Abilities in these battles.