Meeeeh.

I like everything but the 'he saves his friends' bit. And the Yakuza bit. He doesn't seem like a guy that's been a part of the Yakuza. And Shibuya is not a common spot for Mafias and Yakuzas and the like. At least, a nightlife city wouldn't be too good for the role, and Shibuya is fairly active at day as well. So they wouldn't be able to do much without rising suspicion. And his 'he saves his friends' doesn't work for a small Yakuza member, since they'd be assholes.

Yakuza ruins some shit.

EDIT: Just found out, and on the first page of Google for me has 2006-2009 articles about Yakuza in Shibuya. I mean, haven't looked further, so yeah.

EDIT2: And Yakuza aren't as powerful as they are actually depicted in modern media. So, a small city Yakuza = lol wat. And they would probably want to take up a whole region of a city, like the east or north region as a whole is something they'd probably take over. Maybe.