Hmm, I see... this has potential. If I had to continue from here, this would be my idea:
What if the whole "cannot be romanced" status isn't tied to Misaki's gender but caused by his best friend character role? So, as long as Misaki sticks to that role, romance is impossible. Misaki reliquishing the best friend position will allow Hareta to fix this broken relationshop by trying to win Misaki over - but this time, not just as a friend. So forcing Misaki to quit the role of Hareta's best friend would be the hidden way to unlock him as a heroine.