One demon personality can, during recruitment dialogue, ask you what video games you've been playing. If you respond Soul Hackers, he'll respond that he's playing it too, realize that he's at the part of the game where his character is talking to you, and have an existential breakdown. Then he realizes that somehow you didn't have an existential breakdown, which he finds so impressive he joins your party.
The demon negotiations in general are comedy gold. Sometimes, a demon will demand that you speak to them rather than the one you've chosen, some have childlike personalities and will tell you that their demon teachers haven't covered sex yet before asking you how they were born, others will ask for a massage... and then there are the times you successfully recruit a demon only for it to scream that it hates one of your party members. God help you if your demon allies pitch in. "ME FAILED. IT ANGRY NOW." While angering demons gives them a chance to attack, some of the options for doing so are too good to pass up.
Playing Vs. Poker is worth it more for your opponents than the coins. "This hand reminds me of failed experiments."