i played the japanese demo (you can download it without any problems with a japanese PSN account).
you can play pretty much the mission that you see in the trailer. its the same Yakuza 6 / Kiwami 2 engine.
it seems like you are some kind of private detective.
the game is set in december 2018 kamurocho.
the mission starts with a fight between the main character and some thugs who think that you are a homeless guy
but its only a disguise. the fighting mechanics are 1:1 Yakuza.
square is a light attack, triangle a heavy attack,
circle is grab or throw and you can do combinations. this new main character is really really quick.
i would say he is probably three times as quick as Kiryu and the animations are way more complex.
you can do stuff mid air, you can jump over enemies, roundhouse kicks, flying kicks ...
the attacks are more responsible i guess. everything feels more seemingless.
so there are no small stops like if you are playing with Kiryu, its more smooth without interruption.
almost like you are playing a new Tekken or Dead or Alive game. you can change between two different fighting styles i think
but i didnt really understand it because the different fighting style was only for one fight
and of course all descriptions are in japanese.
after the fight you have to walk to a specific spot and there you have to identify the target.
(like you saw in the trailer - you have a photo on your screen and you just have to look around you where the target is).
next thing is you have to follow the target. you know this system from other games.
keep your distance but not too far away and you can press circle at a lot of spots to hide or blend in.
after that you are listening to a conversation and then the main character will confront the target.
now the chase scene begins. the character is running automatically. you can slightly change the direction with the stick,
everything else like jumping, dodging and so on is a quicktime event.
you also have to look where the target is running, otherwise you will lose it.
it ends in a dead end where you have the final fight. again, its typical Yakuza but with a different fighting style.
like a mixture between Akiyama and Majima i guess. then the demo ends.
you can already see on the map that there are all of the typical shops, bars and so on
but its all locked for the demo.
so yeah, pretty much like a story "add on" in the world of Yakuza with new features.