It doesn't feel pity, or remorse, or fear. And it absolutely will not stop, ever, until you are dead
...or captured. Or you give back that MacGuffin. You're being pursued by someone or something. Defeating it is out of the question, any encounter will be a Hopeless Boss Fight. Any "successful" fight just involves delaying it temporarily so you can run away some more. Before I flesh it out more, Do We Have This One??
Hello, Unknown Troper. You'll need to get known to lend a hand here.