On a serious note, I noticed that for joined finales, you can have a player play as one of the girls, which will unlock the finale for another girl that has the player's girl as a secondary actor. Like a couple of make-out scenes that exist in the game.
Not sure if this would work for the player-only characters?
If it did, that would leave the possibility to have Lord Octo as a playable character and girls having special finales with him.
Of course, the problem with this is that Octo does not have clothes. So how would he compete or fail the card game?