Uh, both ig? It's shown in both of the girl's perspective but the main girl is the purple haired girl.
purple girl on the inside of physically purple girl
*or
The purple haired girl (in terms of physical features) is Medea. Psyche is the blonde girl. The main character here is Medea, but Psyche plays an equally important role, since they're swapping bodies. Psyche's role at first is annoying, but she turned out to be a badass girl. So, I suggest you continue reading.
so is the protag were following the blonde which is inside belials body. cause if so I ain't reading this shit