Sean and Laura Matsuda have a very loving brother-sister relationship. While Laura can be very physically aggressive with her little brother, it’s obviously in good fun, even if Sean is an unwilling participant in her antics. Sean seems to be more responsible than his sister, but even he is considered a fun, goofy character by players at large. In essence, the playable Matsudas are, for lack of a better term, adorkable.
As it turns out, characters like this are the bane of lore theorists like me, as they live their lives rather openly. No dark secrets to dig up, no skeletons in the closet, no juicy tidbits that could warrant the characters having a foreseeable dark future. In fact, perhaps the most juiciest thing that I was able to find didn’t really reflect on either one of the Matsudas. Of course, it could have potential implications on future lore. This is the Japanese win quote of Sean to, of all people, Q in Street Fighter III: Third Strike:
“Are you a member of the secret organization you hear a lot of these days?” 「あんたって、最近よく聞く秘密組織とかの構成員じゃないのか?」 https://streetfighter.fandom.com/wiki/Sean/Quotes
This could potentially be a clue to Q’s identity. While this was certainly meant at the time to tie Q in with the Illuminati, with G’s reveal, it could be that the secret organization Sean is talking about is whatever group G is leading. We know Q likely isn’t with the Illuminati because even Gill doesn’t know who he is, which was also revealed in Third Strike. As Gill states to Q:
“Even I, in all my omnipotence, can’t understand… Who are you?”「全能の私にも解らぬとは・・・・何者だ君は?」 https://streetfighter.fandom.com/wiki/Gill/Quotes#Win_Quotes_3
It’s most likely, however, that Sean meant the Illuminati, as Gill ended up revealing his existence on G’s own FooTube channel and got people talking. So, we’re really back to square one again. So, what does Sean’s knowledge of the Illuminati mean for Sean and Laura?
Absolutely nothing.
That’s right. The idea that the Illuminati exists does not affect Sean and Laura in the least. It doesn’t change their stories, it doesn’t affect them personally, and they’re so far removed from anything within the main plot that their inclusion or exclusion in future games has no effect on the series itself.
“But Laura was on Karin’s team when they all went and infiltrated the base!” And what exactly did she accomplish? The Cinematic Story Mode didn’t focus on Laura at all. She was just there. Of course, there’s a good chance there were some deleted scenes we haven’t seen yet that could certainly spread light on the story, but for now, we have to go with what we have.
In fact, even if Laura had a bigger role, it wouldn’t have mattered in the long run, since G appears to be the next main antagonist anyway. And their win quotes to each other also shed no light on the situation.
Laura’s quote to G: “Ha! So much passion! I like your style!”
G’s quote to Laura: “Let us revel in joy, citizen of Earth! All shall share my joy, as they share their joy with me!”
So, Laura isn’t really going to be a major factor in G’s plans going forward. Sean has a better chance to be, but it’s not just because of the quote with Q. In Sean’s Third Strike ending, we see him becoming the U.S. champion, his first tournament win, after training under Ken… only for it to be revealed as an hallucination after getting knocked out by his opponent in the qualifying rounds. https://www.youtube.com/watch?v=DG2nt3rAjbM&t=37s
Laura’s SFIII ending in Street Fighter V, however, seems to directly contradict this.

Fortunately, we don’t have to look too far to realize that Sean likely won a completely different tournament. How? The opponents he faces in the dream tournament he won, the real tournament he lost, and the real tournament he won are all different.
In other words, Sean got stronger under Ken’s influence, and he won a title for it. He would certainly be on G’s radar for this. However, this theory has nothing to do with G despite the ties – this one is a study on the Matsuda Family.
Returning to Laura’s SFIII ending, Laura, proud of Sean, considers this a win for the Matsuda style. However, there’s just one problem with this: Sean isn’t using Matsuda Jiu-Jitsu – he’s using Ken’s brand of Ansatsuken. This is where things start to get interesting, because, as will be shown, Sean shouldn’t really be using it.
In Cinematic Story Mode, Sean and Laura introduce themselves to Ken, Chun-Li, and Cammy. Ken ends up saving Sean from Shadaloo’s thugs, and then fights Laura, who doesn’t take kindly to Ken asking Sean to give him the Black Moons key. When things are finally straightened out, Laura asks to go with the group, and also makes a deal for Matsuda Jiu-Jitsu to be featured in Ken’s online martial arts classes. Laura provokes Sean some more, and he says this:

It’s clear that Sean respects the Matsuda style, saying Laura’s martial art has been altered to the point of being unrecognizable. This is something coming from him, though, since he doesn’t even use it in his playable appearance in Street Fighter III. In fact, he wants to emulate Ken to the point where he’s mastered all of Ken’s techniques.
Quite simply, Sean abandons the martial arts principles of his own family for something he sees as superior after seeing it for all of five minutes.
Impulsivity is what the primary trait of both Sean and Laura is. It’s what drives them both. They have the attention span of hummingbirds, and it makes them out to be complete hypocrites, even if that’s not their intention. They’re both flighty, no matter how mature they try to act, and while they certainly see it in each other, they can’t see it in themselves.
“I can see why you say Sean is a hypocrite, but why would Laura be one too?,” you ask. Simple. She picked on Sean for having a girlfriend (he didn’t) when she herself has scared away every man who tried to get with her. That’s shown in the Side Reader “Blue Christmas in Summer.” https://game.capcom.com/cfn/sfv/column/132150
So, we have two impulsive hypocrites who are trying to go their own way. Laura wants to expand the Matsuda style’s repertoire while Sean wants to leave it alone and pick up something completely different. While there’s nothing inherently wrong with this, both are straying away from the original practices of their family.
And in the end… that’s it. There’s nothing else to really say about the Matsudas at this point. No bad intentions. No dark secrets. Just two young siblings forging their own paths in martial arts and taking opposite approaches. Are they at odds? Sure, but it’s not like they’re not talking to each other. In fact, it’s probably the most stable relationship in the entire series. Sean doesn’t like being tormented by his older sister, but it’s clear she’s having fun and enjoys being in her brother’s company. Sean doesn’t love Laura’s frivolity, but he would still do anything to keep his sister safe from harm and worries about her constantly.

And with that, there’s nothing else I could talk about.

Nope, not a thing.

I SAID, “NOTHING.”