[He wants to follow his gut. That somehow Shigaraki is bluffing and putting up a front about not recognizing him. But how can he be so sure of that since the last time he saw the man it was in the hands of his villains as they escaped. Togata-senpai just barely arriving in time to help them turn the tides and...

He remembers seeing Shigaraki's face. That moment of clarity inside of Izuku started to form at that very moment...

But what happened after that? Would it be true that Shigaraki can't remember? He can't be sure. So he's not letting his guard down. He can't afford that. Not when he has important people here.]

You're ... you're not wrong about that. We know each other.

[Deeper than they really should, that clashing of their inherited quirks.]

But if that familiarity is all you can tell- There's not much else I can tell you. We're both stranded in this world. That's all there is to it.