Hello and thank you for your interest.
Hmm, I don't think you need to play the first game to understand the events in Thorns of War, but as a test you could try downloading the Thorns of War demo. If everything mentioned in the demo feels like it is enough to bring you up to speed and you are comfortable in who your MC is by the end of it, then I don't think the rest of the route will prove a problem.
Many thanks for playing