did you take a bath in your house? 5 times with cum? are you sure it was with cum?
edit: I forgot to say that you also have to talk to annie after taking a bath. You also probably only need to take a bath 4 times.
Here's a guide with pictures
Requirements: Cumlab and cum lover's club unlocked (open at night). Beat dungeon 2 and talk to Freya after.
cumlab. You probably have to get the dialogue where she mentions that you can bring her vials of cum for a better cum treatment.
You'll get the tank outfit here I think. Cum Lover's Club
Go home and wear the outfit. Here's what it looks like. You can wear anything else you want. After this, explore the streets of tale
have sex
get vial
have more sex
more
more
embrace sex
become sex
ok I am done. Just have a lot of sex to have a lot of vials, use the skip button
after having at least 3 vials of cum, go to the cumlab. The highlighted option "Exchange 3 vials of cum" should appear. Get as many as you can, but 4 should be enough (meaning you only need 12 vials of cum)
Go home and select the option "take a bath"
You should see this dialogue box after that "Use one bottle of eau de cum". If you don't, you don't have eau de cum. Select the option and repeat 4 times until you see a flash of your succubus form.
Once you get the flash, go back to the cumlab and talk to annie to ask her about the eau da cum. You will become a succubus shortly after.
I really like the succubus design and I really think it fits the storyline :), I also like the side effects but I don't know if it changes the dialogue.
