At first Natsuo just nods, his throat too tight to speak. It's dangerous, he knows, for Dabi to let himself be this vulnerable in the lives they now lead, and that alone is a testament to the truth of his words. For as much as his cool ferocity is nothing short of entrancing, Natsuo's a bit relieved to see that his brother still has a hint of vulnerability left in him.

Then he laughs quietly, one hand seeking out a patch of healthy skin on Dabi's back to rub comforting circles where he'll be able to feel it. "You're never leaving my goddamn sight again, are you kidding me? You're my niisan. Even if you die, I'm coming with you."

Touya-nii isn't right anymore, and Dabi-nii doesn't quite fit the same way yet, so Natsuo just calls him niisan - but only when they're alone, of course.