[It's an understandable move, considering their situation, but the moment the younger Kaito shifts to raise his weapon, Kuroba moves as well. He steps forward quickly, placing his hand firmly on Nakamori's shoulder and pushing her aside (almost a bit roughly) so she isn't within Kaito's line of fire at all, so the gun is only trained at him should his startled counterpart decide to pull the trigger.

He doesn't let go of her shoulder (he does expect her to jerk away), nor does he flinch as he stares down the barrel of the firearm. Aoko's pleading goes mostly unheard by him, particularly since most of his attention is focused on the weapon: calculating the likelihood of being shot at, the best direction to dart in an attempt to dodge, the possibility of being hit, injured, or something else--]

I don't think you want to do that. [He says it evenly, and then nods at his younger counterpart's Aoko] She has something for you. You should take it-- it will help with the blood loss.