I would recommend the Vigilante Stalker Archetype. The cost of the bushi template isn't bad, and with the loss of the ki pool you'll have plenty of talents to spare. The archetype gives you sneak attack which pairs very nicely with Mithral Current.
With the Daisho Expertise feat turning katana's in to finesseable 2d6 18-20/2 monsters, I highly recommend going for a Dex build with weapon finesse and deadly agility. You can add two weapon fighting to that as well if you like but that will be very feat intensive. Mithral Current style is good for setting up sneak attacks.
I use the Fighter class for my bushi which was basically what a 1E OA bushi was, a fighter with an extra ability to buff himself once per day along the lines of Heroism, I think.