I just imagine that the Ben hiding inside Kylo gets lonely, ‘cause he’s always been lonely, and he’s befriended a little MSE-6 droid that is basically his best friend. It’s a quiet friendship, just an oil bath here and helpful repairs there. It recharges in his quarters overnight, and they pass each other in the hallways of Starkiller, a little nod and a little *beep beep* to each other. They miss each other when Kylo is off-base for a while with the knights or on FO missions. No one recognizes this little droid from any of the other tons of MSE droids, but Ben knows. He’s pretty torn up when he realizes it blew with Starkiller.