[From the half strangled moan Sion responds with that is a very good use for a free hand. Or he could be responding to the teeth and tiny licks.]

[Actually, okay, to be honest he's responding to all of it, fingers gripping Naoto's hair lightly and shivering, pulse quick and watching Naoto with wide eyes because. Wow. Wow. He should just let Naoto touch him everywhere like, all the time. That sounds like a plan too.]