AU where Adult Reborn is the one who is mute. Tsuna, for some reason, is well verse in body language and sign language (from anything and everything to Nana is deaf to Tsuna wanted to learn and Nana encouraged him) is so use to the fact that he automatically starts signing whenever he speaks to someone and can easily answer the unspoken question just by glancing at the person.
So much so, that it takes Tsuna a few weeks to realize that he actually has never heard Reborn speak (while everyone else around him is wondering why this young man is carrying full conversations by himself).
Reborn finds the whole thing amusing and slightly flattering. He’s never met someone who just instantly understands him as if he was actually speaking.
-files this under things I will write even if it kills me-