What sets Key apart from his overeager companions is that he do not relish battle. He relish victory, and total annihilation of the enemy is certainly a pleasant thought, but not the actual fighting. Of course, that is why he leaves the actual fighting to other people.
He had been hearing sounds of battle for a while now, but the view had been blocked by a mountain range. Now that the conflicting armies are in view, he glances casually at the battlefield, looking for anything of note. While a good enough theorist, the lore of the word above Khyber is not his forte, so he is not expecting to recognize much.
He hears the big knight send off their assassin to scout. He would probably have been the better choice for scout duty, but the fact that he spends his time invisible and wordless makes people forget of his existence. Just the way he wants it.
As the girl takes off, he wispers in her head "Bonne chance!
". People still get startled by this habit of his, but she seems not to mind it too much.