Barnaby is starting to listen, so even if Frisk doesn't know, he does. He can hear their reassuring tone, and as he pulls his hands away from his ears to instead tug on his hair, he can hear the child's soft words. All baseless reassurances, but with his name attached, and... and they've picked up the nickname.

Kotetsu's stupid nickname was the one thing that brought him back to himself when he'd been brainwashed into thinking his partner and only friend was a murderer. Now it brings him back from the brink of a panic attack, just slightly, just enough to speak.

"I'm sorry. I'm sorry, you shouldn't have to see this, I didn't mean to..." He breathes out a half sigh, half sob, slumps back down onto the ground so he can bring his knees up to his chest and clutch to them instead of trying to rip out his hair.