It's possible Persephone could be sexually involved in maybe a group sex scene with the player character. If that happens the player will have clearly chosen the dialogue options and menu options to get there.
I'll say it again. Viewable content is selectable via the options menu and also through dialogue choices. If someone finds the idea of group sex icky, for example, they can simply not pursue that content.
Very little will be forced upon the player as far as sex or viewing sexual content goes, as we hope the main plot will be interesting enough in its own right.
-Pelorix