Maybe instead of playing as the girl trying to keep their sluttiness within a certain range, change it so you're the virus trying to get the girl to go out of that range. Reading the dialogues and description gives you clues as to what each girl's "weakness" is so you know how to get them to crack. For example, maybe Roisen can tell Ella that she loves a strong drink, and then later when she's fighting it the virus can suggest to her that she needs a strong drink, lowering her willpower.
When you have more days you can come back to each girl to see how they've progressed in debauchery. So for the first couple days, you're just meeting the characters and can have optional sex scenes if you succeed at tempting them. But you don't get a game over either way. If you don't tempt them, they just aren't as slutty the next time you play as them. Maybe you can roleplay so certain girls go the "pure" route while other girls go full on "corrupted" route, with different dialogue for both. More work, but better corruption.
I love to write this stuff I'd be happy to contribute a little