Tamaki isn't an idiot, but he IS immediately hit with a wave of trepidation. He considers leaving before Tomura notices him, with the hopes of avoiding any kind of actual conflict. That thought is dashed out the window when he's addressed and Tamaki immediately takes one step back.

Wait. They're both quirkless here, right? Sort of at least. They have whatever "magic" this place has given them, but how much could Tomura have handled already? Probably more than Tamaki has, he wagers with a grimace. He hasn't moved any further into the room, but his expression has shifted into a dark frown, an expression in stark contrast to the nerves he's currently dealing with.

"I don't think that's a good idea."