Paige

When a demon attacks and kills one of the three nympths that protect a lake, the Charmed ones try to help. However, once the demon is destroyed, the nypmphs decided Paige should replace the fallen nymph, and they won't take no for an answer.

credit @ chinte10

Paige becomes convinced Cole is still a demon, while The Source, now inhabiting a human body, plots to get Paige pregnant with his evil spawn.