Blood-suckin Sword

Your spaceship just crush into a mysterious and dangerous planet. By radio, you recived a messege from the Central Station. They will come to your rescue, you just have to still alive until they do.

Combat the aliens that tried to kill you using their own weapon against them: a sword that eats the blood of their enemies and becomes bigger and heavier, making you slower but stronger. If the sword doesn't eat for a few seconds, it will retune to the previews state.

Would you be able to survive until the next troop comes?