My guess on who the main lead is always switches between Callisto and Vinter, but plot wise Vinter would have been the better choice. Callisto just seems very one-dimensional and doesn’t seem to have much chemistry with Penelope as has with Vinter.
I think for this type of stories, authors want the illusion of complexity, just to deliver the masses popular one... Always the prince...-.- Who wouldn't want a mage that rescues abandoned children for a hobby????! (And does magic) !???
Tbfr I still don't feel Vinter as the second male lead- am I the only one-?