I agree with a sequel being a good idea but imo it should be a fan sequel given Koda's work ethic.
As for the plot, I could see MC being married and looking to sire his first born with his new loving wife. One night while MC is gathering firewood a monsterous creature attacks him, forcefully taking his seed and part of his soul. When he comes to he realizes he can no longer give children. To regain his ability to give his wife children, as well as to restore his dignity, he follows the creature back to the now broken down hallow mansion. The now disempowered Nora has gone from being a beautiful witch to a monsterous, yet strangely sexy monster hellbent on getting revenge (And some degrading forced sex) from this boy who defeated her all those years ago.