He follows, both because it's rather familiar (despite the sense of unease) and because he can tell it's probably better not to have whatever would be said next heard by whoever was on the road with them.

Luke's still not quite prepared for what Obi-Wan says next, and the sudden, brief sense of sympathetic burning slashing through the join between flesh and artificial hand leaves him gritting his teeth.

"You---"

The suit.

The thought is obvious, and he can't tell if he's angry, disappointed or exhausted.

"Why didn't you just kill him, then?" As soon as the words are out, Luke winces, even if there's incredulous anger bubbling in his stomach still. What was that for sort of question, anyway? And why does he even care, given how Darth Vader is? What he's done?

"I'm sorry. I just---" Luke shrugs, uncertain how to finish that, because apparently he does care.