From what I understood from the game, Leto has not had contact (yet) with any kind of demon or powerful entity that can help him in the final revenge. The entity seen during the dream sequence is just a representation of his doubts and worries about the girls (implying that he is quicker to understand what is going on around him).
My biggest worry at the moment is that the story will eventually reveal that Leto's brief contact with whatever the hell that "artifact" was on the ship during the prologue infected him with some kind of evil spirit — which isn't exactly unprecedented, given the reveal in Chapter 2 that Noah had already been touched by one such entity since the day he was born, long before the story even started.
But personally, I think that would be a
colossal mistake because Leto seems
so much more interesting to me as a protagonist if he is just genuinely struggling with those anxieties on his own without any sort of outside influence trying to manipulate him. And how that would color his potential reaction to the NTR ending, well beyond what we ever got with Noah walking around the village in disguise. From the very first dream sequence that he has of Rose with his two buddies from the brothel, it left me so intrigued by the possibility of Leto having some subconscious fixation. That some small part of him
wants to see that happen, because it breaks the sexual tensions and frustrations that he feels with them without the guilt of doing it himself because he's suffering from a massive Madonna-whore complex.
Also, with all of the Revenge ending chat... I know N_taii has very casually mentioned the possibility of two different NTR endings — one with the girls being exclusive to each antagonist, and another that is more focused on them being "shared" around with other characters — but hasn't made any solid commitments to it because that obviously seems like a pretty significant branch to develop. If that winds up not panning out, I just hope that Chapter 3's version of the Revenge ending might at least dabble in that territory more than with the mostly harem-centric one from Chapter 2, where it was really just Aywin (lucky for me, she was my favorite character by far!) and a couple of the C-list side characters.