Trimps are the main creatures in the game. They are a renewable resource, and can be assigned to jobs. Those unassigned to any job contribute to breeding. They can also be sent to fight on the world map.
The game reveals some story about them.
At the beginning you can send one Trimp at a time to fight. After completing the 10th cell of Zone 1, the player unlocks an upgrade called Bloodlust, which gives the ability to toggle an AutoFight switch which sends Trimps automatically to fight after a certain amount of maximum Trimps has been reached.
After completing each zone the player gets a Coordination upgrade, which increases the size of your battle group. The first upgrade will make it so you send two Trimps at a time, resulting in doubling of their stats.