That is also true! But they're already pretty cozy as they are, Shinji genuinely liking having the steady presence at his back, with that warm voice right at his ear. One of those comfortable advantages the height-boost had given him, and maybe required a bit more indulging in while the opportunity is here.

So, he hesitates for a bit, bashfulness and coziness making an appealing argument to stay right there, but after a moment he lifts one hand away from hugging Kai's arms. Here, let him use that hand to hold Kai's face and twist around juuuust enough to plant a kiss on the opposite cheek. It would be pretty easy to meet him for a more substantial smooch from here, huh?