She was killed by Makima, which was incredibly traumatic for Denji - it's pretty clear he did truly love Power. Even if Power were to make a return, it's unlikely the two would develop a romantic relationship.. It's safe to say that Power loved Denji by the end. I would certainly say romantically, there's just too much evidence to ignore. Denji couldn't feel more than platonic for her for two reasons: Makima (as said above) and the caretaker role he had formed with her after the Darkness Devil incident.
The series ends with Denji and Power departing to hunt devils together while attending high school. While they lack memories of the previous timeline, their bond remains intact as inevitable.. 00:00 - Did Denji and power sleep together? 00:34 - Did power have a crush on Denji? 01:07 - Is Makima in love with Denji? 01:32 - Does ghost die on power? 02:00 - Does Denji kill.