He's changed his mind.
Hisoka sees it when he pulls back. He's specifically looking for it, and when he finds it, it rips a hole in his stomach and spills his intestines all over the floor.
He's never admitted it to anyone, least of all himself, but for as much as Tsuzuki hates his eyes enough to try to gouge them out with back alley glass shards, Hisoka loves them and has loved them since that day Tsuzuki winked at him in the rain. I changed my mind. Looking forward to working with you.
He loves them because they're so expressive that they do the work of his overactive paranormal brain for him. He doesn't have to be touching or even near Tsuzuki to read what he's feeling; from a safe distance ten feet away he can glance at Tsuzuki's face and tell exactly what he's thinking based on the light (or lack thereof) in his eyes, or gauge his mood from the exact manner in which his gaze is cast down to the floor or upturned toward heaven. He knows which of Tsuzuki's tears are born of happiness, of disappointment, of allergies, of grief. Even when they're closed, the power of those eyes shine forth unmitigated, illuminating his face, telling his intentions plain as day.
Like now. They're shut lightly, affecting calm, but it's a forced peace; sentries posted on a castle wall with only half-hearted interest in keeping the rabble in line. Sandwiched between the lids, decorating his lashes, is the line of It's all right now, Hisoka; I'm tired saltwater that Hisoka had desperately hoped Tsuzuki had cried out and had done with. What's left of his stomach seizes up, sending a gnawing awfulness up into his heart and throat.
What if that's never going away?
"Tsuzuki…" Hisoka somehow manages to choke out, even though Touda has eliminated all the water in the air and in his throat already. "Tsuzuki…"
The knee he'd been trying to get a better balance on trembles and gives out underneath him, and not for the first time the only thing holding him up is Tsuzuki's presence. On some level he's aware that he had ceased being coherent, that he had slipped into the same desperate sobbing as when his mother Rui dragged him by his hair and arm from the table to the basement; as when he was finally let out and he ran to Nagare seeking assurance that this time was truly the last time this was going to happen; as when he fled to the graveyard afterwards to throw a tantrum at Hisoka-oneesan's headstone before dissolving into a flood of please come back please I can't stay here alone.
It never worked then, and after it failed to protect him from Muraki he told himself that it never, ever would in the future, but he couldn't stop himself from doing it now. It wasn't like staying aloof helped him any when it came to Tsuzuki. In fact Tsuzuki has already seared himself into Hisoka's mind as the only person who he can break down cry break down in front of safely like this; Tsuzuki is special and good and astonishing; Tsuzuki is unlike anyone Hisoka has ever known and will ever know and maybe Tatsumi is right, maybe Tsuzuki should have this rest that he obviously wants; this longing that comes from a place in his soul that Hisoka doesn't know if he'd ever be able to touch, let alone heal, since he hadn't even been able to see it until hours before. Maybe Tsuzuki deserves it, deserves better than what he has; deserves everything he wants.
Maybe—Hisoka thinks suddenly, from a place he didn't know he had within himself; from a place Tsuzuki had been unwittingly cultivating for the past two years—maybe Hisoka does, too.
"I am not going back without you!" Hisoka has to shout, because he can barely hear himself now over the roar of flames, but inside he is calm, steadfast. He feels Tsuzuki tense up to push him away, and he struggles against it; one hand planted on the wall supporting them; the other digging into Tsuzuki's skin through his clothes.
"I will never let go of you again," Hisoka manages to grind out, pushing back against the hands that are trying ever harder to force him off with a sudden burst of adrenaline that Touda can't slow down. All he can think now is that he's already been made to let go of his family, his life, his dignity, and any good thing that's passed through his hands during his eighteen short years of existence, and he will not be sent or dragged away from what he wants more than anything by anybody ever again. Not even by that thing himself. "Wherever you're going, I'm going with you."
Somehow that's it, the thing that gets Tsuzuki's hands to fall away from him and his eyes to open, and whatever Hisoka was going to say next fails to pass his throat, because while it's watery and faint and almost shined out by the light of the inferno around them, they're dimly alive with a feeling Hisoka realizes he's never really seen in them before, not to this level of stunned security, of incredulous full comprehension.
Loved.
When darkness covers them Hisoka isn't sure whether it's Tatsumi's shadow or his body succumbing to death. What he is sure of is that, whichever fate waits for them, this is the feeling that Tsuzuki is going to take with him into eternity, and that he's the one who gave it to him, and that no matter what he spent two years thinking he had to do to reclaim the pieces of his soul that had been taken from him, this fact is what put him back together, even without them.
When he wakes up, this time surrounded by white and cool, he thinks he's in Heaven. When he turns his head and sees Tsuzuki in the infirmary bed next to his, violet eyes gazing softly but no less intently back and telling him good morning and please be okay and thank you, so much, he knows he is, and that he is never leaving.