This world is the same as ours. Almost. The physical geography coincides completely. The political one is a little different from our Middle Ages. Not too important. Technological progress was similar. Not exactly, so rivets on the topic of correspondence to the era are not accepted. There is one fundamental difference. Humans have a recessive gene. Full carriers of this gene can change their appearance at will. No, they don’t become wolves or bears. Facial features do not change very much. But fangs and claws appear, capable of tearing the best steel, and short hair on the body. At the same time, werewolves become much faster and stronger. Including speed considerations. All skills acquired by a person are preserved in the Appearance. They are called differently in different countries: wildver, berserkers, velet... In some places they are not called at all. And in some places they are not there at all. And they are treated differently. Some save it, some use it. And some people consider them evil spirits. But they are who they are.