This is something I've been working on in Koikatsu studio for the past couple of years or so, A sort of hypothetical visual novel/dating sim CG set using mostly just the default characters, one or two OC's plus some other random cards I've picked up here and there
It's divided into 4 acts, each with their own genre, in this Third instalment, the PC's mutation has turned viral now the reset of cast are rapidly growing dicks of their own!
The basic story is that the main character Chika (she's the default creator Character, so I thought she'd make a suitable protag) is the local omega wolf and volunteered to test some of the school nurse's new experiential medicine, the result is her developing a pheromone gland capable of producing a powerful aphrodisiac through her sweat.
In Act 3 further attempts to cure PC's penis growth have resulted in her mutation turning into a contagious virus! Now any girl who comes into contact with her cum or precum will irrevocably be futarized themselves...... all it took was a pep talk from the school nurse for Chika to realise this was a blessing in disguise.
And So Chika sets out for a third time, to spread the joy of being a futanari to her 50+ circle of friends and fuckbudies, meanwhile the nurse eagerly gets to experimenting with a few unwilling test subjects of her own, to create what she calls a "true hermaphrodite"
*Update* Added a bunch of bonus scenes to all 4 parts and split parts 3 and 4 into two separate galleries each