The phrase that most establishes tension is:
"Ulrich von Gradwitz patrolled the dark forest in quest of a human enemy."
This phrase creates a sense of conflict and danger, indicating that the character is not merely hunting for animals, but is instead on the lookout for a person, an enemy. The mention of a "human enemy" implies a hostile situation and suggests imminent confrontation or violence, which heightens the tension in the narrative. The darkness of the forest adds to the suspense, as it implies uncertainty and hidden threats.