The cavern isn't an ideal place to wake up naked ...isn't an ideal place to wake up at all, but it's the dish fate served them at this juncture. Byleth had reacted to the abrupt change in scenery with a lot of trepidation at first but is managing to keep calm and level-headed, if only because he recognizes panic isn't going to do him a lot of favors at the moment. Better to assess the situation, then figure a way out of it. His father would have likely instructed him to do the same were he still alive.

Running into someone else naked is quite unexpected as well, but Byleth knows how to keep his eyes firmly in one spot when he has to. He's spent enough time bathing around mercenaries and soldiers that this truly is nothing new to him, even if he can't say the same for the cave's other occupant.

His hands eventually rise to show he's unarmed as he approaches a few steps with the same care he'd show were he approaching a wild animal.

"Stay at ease. I mean no harm. I've also just arrived."