Requirements is that you finished save the master and did the beans drink quest for the unnamed hell hounds you can get an event
so I had this dream where if you enter hell (idk what it’s called) and you enter the love hotel place where you can offer yourself for the purple currency the owner of the place will come up to you and ask you if you would like to help with the guest book at 12:30
once you go there he gives you the guest book and you start to scroll through the names and in doing so you find the hell-hounds and you can have the option to ask if you could be the one to assist him or to just continue with the guest book
If you ask to assist him them: you enter one of the rooms and after a bit of waiting the bell hounds enter and you strike a conversation leading into a sex scene
if you continue helping with the guest book: nothing happens and you get the normal sex scene with all the demons