The Hunters are those in charge of gathering foods. The Mice and Cats made the hunter entire force.
The Hunters bear the mark of "Benevolent Sun". It's a symbol of the sun that keeps everything alive. Just like the hunter, without them the Union might face shortage of food very soon.
The Mice are tasked with collecting what's on the land and up. From plants, to fruits above. Their small nimble body allowed them to reach places that's normally inaccessible.
The mice also received formal combat training from the Wolves in order to hunt the Animas, huge feral monsters, for food. This made the Mice had a tight bond with the wolves. The Mice view the wolves as those they should respect, and the wolves views Mice like smaller brothers that they should protect and teach to be as strong as them.
The cats are those in charge for food under the water. From rivers and the sea.
At first, they are completely outclassed by the Otter tribes who are far better swimmer and diver. But in turn, the cats invented many fishing tools and techniques that made them on par, if not better than the otters who stayed with their traditional ways.
Not only fishes, the cats also invented many dishes based on everything found on sea. They are adventurous and love to experiment, thus the reason why they advance the fastest not only among the Union, but the rest of the tribes in Gaia.
Of course, the otters hates the cats with passion. The only reason the Otters refused to join the union was because the Cats are also in it.
The cats also loves layleaf even more than every other tribes in Gaia. This creates a strong bond between them and the bats.