The Tigress are a race of anthropomorphic part tiger, part human creatures that live in the large forest north of Anima Town in TSWCAtS. They aren't completely covered in fur like most anthropomorphic creatures, but they have cat ears, cat tails, feline eyes, claws, slightly pointed fangs, and sometimes stripes or spots on their faces, arms, and legs. Despite the word "tigress" referring to female tigers, there are male Tigress.
The Tigress have a strong disliking toward humans and are often at each other's throats, though they have tried to live together in peace in fear of a war, which eventually happened. They often mess with any unfortunate humans who stumble across their forest and try to turn them against the humans, attempting to convince them into becoming one of them. Humans can be turned into artificial Tigresses if they drink a certain magical elixir. One example of one of these artificial Tigresses would be Princess Terririn.
One of the ways they are said to get people to join their tribe is by force; abducting small human children and turning them into Tigresses, raising them as their own. This may be a myth made up by the TSWCAtS civilians, or maybe perhaps a rumor that the Tigress themselves purposely spread to the civilians so that they wouldn't go near their forest, not wanting to be disturbed by the humans.
Despite how mischievous the Tigress tend to be, and how malicious the humans claim they are, they're not really evil. They're helpful to those in need at best, and malevolent at worst. They're generally neutral - they're used to having a strong disliking towards humans, but if a human that had not personally harmed any of them was in desperate need of help, they would likely help. Of course, there are a few that just absolutely hate every human and are entirely prejudiced, but generally speaking, they won't hurt a human if they haven't done anything to provoke them.
The Tigress are only capable of using black magic, so they are restricted from most spells that normal wizard humans can do. But they can use their own magic, which is very similar to regular sorcery, but it has a darker sort of tone to it with more side effects and consequences.
The Tigress also apparently aren't affected by certain afflictions that humans can have, evident in Terririn's story when she was turned into a Tigress solely for the purpose of being cured of her fatal illness.