it would be a very spur of the moment kiss, theyre not even really together at that point. its likely how lumen would want to thank her for protecting him, believing in him, training him, after they escape some kind of operation together, just the two of them separated from the rest. he would push aside the veils on yokais hat gently, ask her if thats ok, and she'd nod quickly.. and he'd inch his face a little closer and ask again, and she'd nod again, nervous.. and he'd touch her face softly and lean in to close the distance for a very private and tender first kiss between them. probably his first ever. not hers, but definitely the best one shes ever had. she gives him the confidence to make the first move.