Ok, so there will be a spell - much later in a story, but first you will meet some weird alchemist researcher who makes unstable futa potions, you could help her, or steal her research (and complete potion for your own gains), or you can destroy this research through plotting with some professors.Future tags are futa/trans?
Since the protag is a mage I assume it's a spell to make herself have a dick or if the protag is male a spell to cast on his apprentice?