Okay so, this update was insane, Endo saying "You'd be better off giving up on him" gave me chills I swear, this shit is bad.
Lime that any of my theories could be true to this, but also, the Red Chanpuru logo is three damn dragons, and mister "there's an ancient chinese dragon sealed under the eyepatch/in my right eye" is linked to it, is that a way of saying "those guys took my eye" because hello?!
Now, my wonderful mutual @cringe--is--dead and I have been talking, apparently Red Chanpuru is an Okinawan dish, a stir fry to be more specific and Chanpuru means "something mixed". There's a high chance this gang is Okinawan, which explains why they couldn't find Suo from middle school until now after he possibly escaped all the way over in Makochi.
Now, Okinawan people don't consider themselves to be really Japanese, so the way Suo delivered that "No, I'm Japanese line at the beginning" makes me think he might in fact be Okinawan, Okinawa also has a lot of American influence and mix due to military bases, so suddenly Suo saying his name is "Leonardo DiCaprio" and talking about the dogwood tree meaning in English might make more sense, Suo might be mixed.
Overall Suo as a character is a mix, a mix of cultures (Tea-cakes from over the world, use if English casually, Chinese clothing...) uses mixed martial arts and is the perfect mix of mature and childish....
On top of this, and I swear I need to study Nii-sensei's brain, the Hayato people (known for martial arts) that Suo is named after lived in the Kyushu region of Japan, of which Okinawa is part of.
And if that wasn't enough, the sappanwood three of where the red dye "Suo" is obtained is historically important for Okinawa, and not only that, the largest sakishika sappanwood tree is located in the Higashi village in Okinawa.
Nii-sensei is very careful about choosing his names, and this feels like it can't just be a damn coincidence.
Suo's secret language could be Okinawan dialect, apparently it is distinctive enough to be considered an actual language instead of a dialect of Japanese, but could also be Mandarin or Cantonese he learnt from his master or even English is he's mixed.
I still think his master helped him escape.
But also, Suo being Okinawan would work so well as a parallel to Sakura, he would also be an outsider to Makochi, and I think Sakura does in fact have a bit of an accent because of the town he's from, Suo doesn't use his dialect which is a further show of how much he hides himself while Sakura is just unapologetically himself. It does explain how he was directly drawn to Sakura as an outsider himself.
So many more thoughts in my brain now, and I love that the sect/cult adjacent organisation and the underground fighting rink theories could still be true.
Whatever it is, this gang is likely from outside of Makochi and came here to find Suo.
I have to do some more research on Okinawa and some things I've noticed regarding Suo, but I needed to get this out now.