Denji’s surface-level motivation is his desire to touch Power's breasts, but his deeper empathy for her loss is what truly drives him to help, despite her eventual betrayal.
Makima explains that a Devil's strength is directly proportional to how much its name is feared by humanity (e.g., a "Car Devil" is powerful because people fear accidents).
Seeking to rescue Meowy, Power lures Denji to an isolated house to sacrifice him to the Bat Devil . However, the Bat Devil betrays her as well, swallowing both Meowy and Power. Worldbuilding & Power Systems
The episode establishes that despite their friction, Denji and Power are remarkably similar; both have lost their only meaningful companion—Denji with Pochita and Power with her cat, Meowy .