I did some research into this last month as I was looking to move to either Tokyo or Osaka at one point.
The only Arcade/ Prop firm I could find is Jane Street Capital.
Jane Steet Capital
I got an acknowledement from the HR department when I sent off my CV and covering letter, but that's as far as I got .....
There was another prop firm called Orbixa (formerly Swifttrade), but I have a feeling they've gone under, as I couldn't get any response whatsoever from calling/ emails.
You could also try looking on the 'Banking and Money' page of Gainjinpot.com
Gaijinpot
Good luck