You can check with the fortune teller, find a way to interact with the succubus girl and the merchant who looks like a demon, periodically changes the store address and has a short name. Think about it.
If you need succubus-style clothing balls, Selena gives them to you when you exit the Dream World (50% chance) and you can buy them at L's shop (mystery item, more than 500 coins). If you meant the spell, you need to complete the quest with the main demon in the swamp and with Domenea.
