I feel like I haven't seen any crack-played-straight fics where a male character gets turned into a female via magic.
Noctis gets attacked by some daemon. At first it seems like whatever spell it was only gave him a headache and stomach cramps. He goes to bed feeling unwell. Wakes up next morning missing a penis and having gained breasts and a vagina overnight, proceeds to freak the fuck out.
Up to you if you want to play it humorously (or kinky, if maybe Noct is feeling adventurous and wants to take advantage of a one-time opportunity for self-lubricating sex) and have them find a cure, or you could go the more serious rout where the change can't be reversed (in which case, I'd want Noct to still think of himself as male and to still be addressed as he/him by his friends).
Noctis gets turned into a woman
Noctis gets attacked by some daemon. At first it seems like whatever spell it was only gave him a headache and stomach cramps. He goes to bed feeling unwell. Wakes up next morning missing a penis and having gained breasts and a vagina overnight, proceeds to freak the fuck out.
Up to you if you want to play it humorously (or kinky, if maybe Noct is feeling adventurous and wants to take advantage of a one-time opportunity for self-lubricating sex) and have them find a cure, or you could go the more serious rout where the change can't be reversed (in which case, I'd want Noct to still think of himself as male and to still be addressed as he/him by his friends).