Trinity:Creature Mementos
A Lynaen word, memento is the term used to refer to the creatures used extensively by trainers.
Background
Mementos began originally as normal, wild animals, native to the plains of Sarteri. However, when the halflings were under attack by prophet moths, they needed to arm their children with something less prone to friendly-fire than firearms. As such, a training method was developed, and the reins of wild animals were put into childrens' hands.
Time passed, and the children moved on from attempting to tame and teach these creatures - but not all did. Rather than take up the call of the gunslinger, some of the halflings devised breeding methods, as well as more advanced training techniques. They improved upon the gnomish methods, and clarified the creatures' connections to the Blue.
Within several decades, the creatures were no longer recognizable as natives to the region. Instead, they had been turned into a classification of animal known as mementos.
Today
In the modern world, these creatures are raised in Sarteri and Chaliraz on small ranches, where one or two halflings tend to them, continuing to breed the same creatures their people have been breeding for centuries. It is tradition for those who take up the path of the trainer to be gifted with one of these creatures, as they are unusually powerful and fierce for their size - such is the power of selective breeding.
Not all trainers come across their mementos honestly. It is not even necessarily a requirement for a trainer that they use a memento.