
Ok, so Haruna is an angel by birth. Like he always is like this and always has been, and Enamoto knew this. It seems Haruna has a physical body that others can interact with, but he's not a normal mortal by any means. This was apparent when all normal humans (Souma and that weirdo) got noosebleeds before fainting due to Enamoto's tantrum.
In this last chapter we learnt that when Enamoto died he kind of already had it in his mind that he wanted to know if he had a chance with Souma, and if he did, he wanted to make sure Souma would choose him over Haruna. So he said that for him (Enamoto) to live, Haruna would have to die (might have been a lie).*
So Enamoto deserves a bit of an ass kicking for messing with Souma's feelings.
Anyway, turns out that all Enamoto really needs to fully come back to life is to have a strong will to do so. For that he needs a reason and that reason seems to be Souma ╮( ̄▽ ̄)╭
* So I wrote this in the replies then accidentally deleted it but:
The deal Haruna made Enamoto might have been this:
A) Haruna dies and Enamoto lives.
or
B) Enamoto saps all of Souma's life, thereby killing him, and then Enamoto can come back to life.
That's what Haruna might have meant with "using" Souma, and also why he said Enamoto would choose neither option (Death of Haruna vs. "Haunting" Souma).
But there's a loophole: If Enamoto wants to live with Souma strongly enough, then he can come back to life without killing anyone (●'◡'●)ノ

Spoiler below!
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I tried to make sense of the translation. I think I was mistaken about the part where either Enamoto or Haruna has to die part.
My best guess is that Haruna made a deal to make Enamoto stay alive which meant:
A) Haruna dies and Enamoto lives.
or
B) Enamoto saps all of Souma's energy, thereby killing Souma, so that he can live.
That might be what Haruna meant by "using" Soma and that Enamoto would choose neither option.
The loophole was then to want to live with Souma so badly, that he'd come back to life (●'◡'●)ノ

I believe the strong attachment part was only to make his soul still linger longer. if he didn't have any kind of regret/want to meet souma, haruna wouldn't have been able to hold on to his soul that long. idk if a stronger attachment would actually bring him back to life though but that's probably how it will go

Yeah, the attachment was necessary to keep him around in the first place. But I have a feeling it might be more malignant than we think. I mean, remember when Souma got his nosebleed and Enamoto began to panic and apologise, saying it was all his fault? After this chapter, I'm starting to suspect that he's kind of like a supernatural parasite; eating up Souma's lifeforce to maintain his own.
I think that's why Enamoto feels so torn. Because if the haunting is benign, I don't see a reason for him not to stick around Souma. I mean, they like each other.
As for how he'll come back to life; yeah, we both know the ending. But the logistics of it? Only guessing ┑( ̄Д  ̄)┍

I remember when they were telling about their most embarrassing moments in ch.82, but both were sugarcoating them. Cirrus just said he peed himself in class and Skyler talked about being drunk and making a fool of himself in front of a friend. I think they both will tell each other the whole, dark truth this time.
It's nice to see their relationship deepen and mature ˗ˋˏ ♡ ˎˊ˗

Yeah! It felt like both of them wanted to be honest, but couldn't bear to do it fully quite yet. It was too risky.
Even back in ch. 82 I was quite surprised that they were willing to show themselves so vulnerable, although neither of them understood just how much the other had exposed themselves by even hinting at it. Both of the instances they mentioned were connected to deeply rooted trauma that changed their personality. At least in terms of how they acted in public. And now Cirrus trusts Skyler enough to tell!!
It's just ˗ˋˏ ♡ ˎˊ˗
OooooooOOoooo~ seems like mutual attraction is in the air~