Peace happens the way it should, (with Izuna living after Hashirama saves him) and all through peace talks Tobirama never speaks a word.
The Uchiha notice him using hand signs, but they all just assume that's so they can speak without the Uchiha knowing what they are saying. They are doing the same so it's a logical conclusion.
But now it's a year into peace and it finally occurs to Madara and Izuna that they have NEVER heard Tobirama speak.
Once they reach this conclusion they start paying attention and they realize there is always a Senju around him that will talk for him.
His secretary sits at a desk in his office though right by the door instead of back by the window and she will respond to any questions being asked. And if she doesn't have the answer she will tell them to come back later when Tobirama has time.
Touka, Hashirama or Mito are almost always with him when he is away from his desk.
And if he is walking around in the village and someone asks him something a random Senju will suddenly be there answering whatever is asked.
When he is given a kind greeting he will smile and nod. But never speak.
And he never goes on a mission with anyone but a Senju, if he has a partner that is.
Everyone has always assumed he was just kind of stuck up, or possibly very very awkward in a social situation. No one would call him shy of course. But they really don't have a better word, so they go with awkward.
But now Madara and Izuna know. They know it's more than shy, more than awkward.
So Izuna does whatever ration person would do. Shows up unannounced at their home and ambushes Tobirama. Starts with accusations of him being defective, or a liar, or too full of himself and racists to talk to people outside his clan.
In full view of Tobirama's protective sister in law.
Izuna opens his mouth again about to say something else unadvisable when Mito unleashes a wave of killing intent never before seen from her.
Madara was chatting with Hashirama in his office when they feel it.
Both of them shoot up and head straight to Hashirama's home.
Where they witness Tobirama holding Mito back from murdering Izuna, whose face is now sporting a huge shiner.
Mito is spitting mad. Swearing at Izuna with words that should never be repeated.
Madara's and Hashirama's jaws drop at the vile words she is spewing.
Tobirama stomps his foot twice and that spurs Hashirama into action and he takes over calming Mito.
Madara looks down at Izuna who hasn't gotten up from the floor.
"I may have, possibly called Tobirama defective for refusing to speak."
Madara slaps a hand to his face. "What is wrong with you?"
"I wanted to force him to tell the truth, to actually respond!"
Hashirama interjects at this point, "Tobirama is mute. How did you not realize that?"
All three Senju look legitimately confused.
"How would we know that? You say that like it's common knowledge!"
Tobirama makes a few signs to Hashirama who nods back.
"It has never been a secret. He has a secretary who does all his talking for him. He seriously has someone with him whenever shopping! It's not as if we were hiding it!"
"Trust me when I say this. But NO ONE knows that."
And they discover the next day that the Uchiha were in fact correct. A year after the village was built and not a single member of any of the clans knew Tobirama was mute.
They all, like the Uchiha, mostly just thought he was rude.
Once the cat is out of the bag all the Shinobi decide they need to be able to speak with Tobirama and learn to sign so they can understand him.
Which leads to opportunities for people who are deaf in the village. They finally have an easy way to communicate with everyone in the village.
Once Madara learns to communicate with Tobirama he finds that he enjoys the other man's company. And surprisingly that he has a great sense of humor.
A year after the discovery Madara works up the courage to ask Tobirama out to dinner, just the two of them.
Once they have finished eating Madara slides a box across the table to Tobirama.
Inside is the most beautiful hunting knife Tobirama has ever seen. When he looks up Madara signs to him "may I court you?"
Tobirama blushes a deep red and nods with a shy smile.
Longer story can be found here
https://archiveofourown.org/works/64701658