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Shouto is the kind of person that, thanks to his calm demeanor, can blend quite well among their friends. Nobody questions when he keeps to himself and everyone is eager to hear him talk, but at his own time. A presence that you know that’s always there, not quiet in the background, but not in the spotlight either.
When Shouto discovered he could do that, he took the habit of friends-watching as part of the efforts to understand people better, specially his class, who was constantly helping him on his growth as a person and as a hero. Also, he really liked watching them interact, because that way he could learn little details about their personalities that most people didn’t notice often.
He discovered a lot of things, like a little tick on Kaminari’s right eye whenever he is overdue to discharge some energy from his quirk, or Kirishima’s left hand drumming while watching the tv. He also discovered Mina’s habit of bringing sweets whenever she comes back from an outing, and that Tsuyu’s soft hums when she is studying are always the same tune. He discovers that Satou’s most tasteful pastries come out of anxiety, and Jirou sits upside down when she’s bored.
In one of his evenings friend-watching, Shouto discovers that Bakugou and Midoriya have the same thinking face, but Midoriya covers his pouty lower lip while looking down on his notebook and Bakugou just stares into nothing with the same pout. Their expressions are so similar, it intrigued him. Surely it isn’t a coincidence, being childhood friends at all, that they share some mannerism, but something deep inside his brain tells him to keep watching them, because he knows they have more similarities.
And, sure enough, Shouto kept finding things that his two best friends did in a similar way like, even if they are not in the same work group or not even shared study time on the matter, when talking about their homeworks, their answers have the same train of thought and arrive at the same conclusion. It’s more evident when they are revising together, because sometimes one starts an idea that the other doesn’t even need to finish out loud to arrive at the conclusion, leaving everyone around them asking about the missing parts of their silent conversation. Shouto chuckled out loud when Sero and Mina were subjected to that.
Curiouser and curiouser.
With those two discoveries, Shouto develops a separate hobbie: watching Midoriya and Bakugou as close as he could without disturbing them, so he can find every similarity they have. He knows there’s more, because his brain provides them with little instances of them in the past, so the two-toned boy wants to learn them all. He thinks that’s a best friend level of knowledge he must acquire.
He learns that both of them eat their breakfast from hotter to colder food, but they place it in a mirror way, almost like if they were sitting in front of each other, even if it’s not the case. That discovery took Shouto a week to put together.
He learns that, even though Midoriya has every color of the rainbow in markers and Bakugou don’t, both of them use the same specific way of taking notes. That discovery also led him to learn that it’s not just them, because Jirou, Kaminari, Momo and Tokoyami use the same since their Cultural Festival. Maybe they learnt it from the same source.
The most interesting discovery Shouto makes is while on a mock up battle training.
They were put in pairs and had to capture another pair in a 2v2 battle. Midoriya and Kirishima went against Bakugou and Sero. The poor bystanders in that battle were easily captured by the half of the Wonder Duo that went against them, but that match ended in a tie because Midoriya and Bakugou kept reading each other’s movements like they already knew it by heart, and one would assume it could be the case, since they train together almost every day, but both of them were keeping the other on his toes while also shouting praises on some new addition or another to their attacks.
Aizawa gave them another chance, pairing them together against Shinsou and Monoma. That match was a full discovery by itself because, when Bakugou and Midoriya fought each other, they talked non stop, taunting each other or commenting on every move while dodging it but, when they were working together, they were silent. Some may think they were being cautious about Shinsou’s quirk, and they could be right, but Shouto could see there was something deeper there, because it was like they were reading each other’s mind, with a little hand move or a nod as their only type of communication.
In the end, Midoriya and Bakugou captured Shinsou and Monoma faster than any other pair. Bakugou screamed their victory at Monoma’s face, while Midoriya talked with Shinsou about some move that almost broke their defenses.
“You are like twin stars,” Shouto said to them when they joined their classmates on their way out of the training ground.
“Hah!?”
“E—Eh?”
Both of them went the same shade of red in the face, exchanging frantic looks between each other.
“You are like twin stars,” Shouto repeated, like it was enough explanation, until a different idea came to his mind. “That or both of you are hiding a mind reading quirk”
“A mind reading quirk!?” Izuku squeaked, looking frantically anywhere but at Shouto’s direction, in an attempt to find an escape route from the situation.
Katsuki huffed a laugh at that, less flustered than the green-haired boy on his side now, but still trying to mask his surprise at Shouto’s commentary. “Nerd’s got ‘nough quirks on his own, he ain’t need more”
Shouto narrowed his eyes, looking intently between Midoriya and Bakugou. “Then you are twin stars. It’s the only logical explanation” he said, just outside of the locker’s room.
While changing out of their hero suits, Shouto sit across the other two, Midoriya going on a mumbling nervous spree and Bakugou huffing an undignified sound from time to time, they were still working in tandem, taking out the same things at the same time and placing their showering stuff on very similar baskets, the blonde’s a soft moss green and the freckled boy a vibrant orange.
“Oh” Shouto let out, cutting Midoriya’s mumbling attack. “Oh I was so close”
They were soulmates, Shouto could see it now. The things that were supposed to be similar between them were a conversation, not a copy.
With that new discovery, Shouto smiled at himself and went to shower, while his friends called for him. He decided to stop watching them so closely from then on. Either they didn’t know or didn’t want anyone to know, and it was not his place to say anything anyway.
Three years later, at Bakugou and Midoriya’s apartment, a proposal was made with Shouto’s help, and in his ‘best man’ speech at the ceremony, he talked about his discovery, making everyone cry, even the stoic Katsuki.
Shouto was right on two things that time in the locker room: they were soulmates and they didn’t know yet but, just like anything else, they figured it out together in their special kind of way.
And if Shouto was the voice of reason from both of them on more than one occasion while they were yet to be a couple well… you had to be looking very closely to pick that up.