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).
The episode hints at a larger geopolitical landscape, mentioning that other countries like the Soviet Union (which still exists in this timeline) are weaponizing devils for military use.
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.