He actually had a role in story mode and that still shocks me, especially how it basically makes him impossible to remove from franchise lore because everything he does is MASSIVE.
Heihachi’s wife was actually the original source of the devil gene, having it herself (apparently they’re just going to ignore whatever the fuck was up with Jinpachi in 5), and Heihachi killed her when she attacked him as a demon and revealed her plan to curse his family. This is also why he threw Kazyua in a volcano, fearing he had the same gene (and he did).
Akuma gets dragged into the rich people with problems start world war 3 drama because he knew Heihachi’s wife, saying she saved his life once, so he’s fulfilling a request she made to him - kill her husband and son.
This is massively important because after Heihachi realizes Akuma is going to go after Kazuya as well, who he’s currently at war with (as in very literal war), he decides to use Akuma by simply taping Kazuya and Akuma fighting, since in order to beat someone as strong as Akuma, Kazuya has to use his devil powers. Needless to say, that freaks the shit out of the public.
Akuma’s entire presence in the story basically becomes the catalyst to end the battle between the two once and for all, where Heihachi finally dies and for real, the single biggest story beat in the series since…well, ever.
In other words, everything that’s going to happen in Tekken 8 is ENTIRELY BECAUSE of Akuma’s involvement.
Oh and I’m iffy on Akuma being the echo fighter because he has a few moves iconic to him that might be a bit much for that, but we do also have Dark Samus around so who knows.