The voice is definitely a surprise and Yosuke feels slightly stupid for jumping at it when he actually got a reply to something he said. He blames it on the room's unpleasant atmosphere. At least he can rationally conclude that if no one else had returned from the room dead or harmed, he'd probably be safe sitting on a normal chair like the one that appeared.

"That works."

As he does, he'll put his kunai back into his pockets. They're still near enough for him to pick up if needed, but at least he'll trust this guy enough not to look like he'd jump at him for every move...

"So, who are you?"