[Katsuki nods, silently, when Izuku asks if he really was so bad off that Izuku thought he died. That's what he was told, and what he remembers was pretty damn bad. He doesn't know what he actually looked like, while he was on the battlefield, but he knows what his scars look like, and remembers how soaked in blood his Hero costume was. So he can only imagine... he probably looked like a walking corpse.

In order to really explain, and be open, Katsuki moves (with just a little difficulty because of his one arm) to pull his shirt off over his head. To show Izuku the scars on his chest and back. How... huge they were, and gnarly.

How it looked as though he had been shot by a gun point blank. And if Izuku were to feel for his heartbeat, he'll feel that it's... slow. Barely there since becoming a vampire. But beating so strong and defiantly despite it.]

He tried to destroy my heart. Went right for it.

[He can't remember exactly what happened, just that he was in front of Shigaraki and then there was a blast of pain and his vision went white...]

Best Jeanist and Edgeshot were there to take care of me, though.

I... I dunno the full details, but from what I was told Edgeshot used his Quirk to spread his body thin and stitch my insides together. He kept my heart and lungs from falling apart.

[If he was just a little further on the timeline, he'd probably have everything explained to him in full detail by the doctors and witnesses around him. But he didn't have time for a whole biology lesson on how he survived while on the battle field.]

I survived thanks to him.