When you play Yuffie (4), you can search for a Shuriken anywhere in your deck and put it on her for free! Then, she gains Haste and so can immediately attack for a second Shuriken! Now, she can't be targetted by effects, she can't be Blocked by most things that can beat her and she can't be chosen by opponent's effects!
Even if a sacrifice Block appears, if it's Power is 5000 or less, you can just throw one of the Shuriken at it for 1 guaranteed damage! Or, if there's a nasty Forward hanging around, two 5000 damage hits will take Break of almost any Forward!
Yuffie (4) will combine well with Yuffie (5). With Awakening, you could even get Yuffie (4) out cheaply on the second turn from anywhere in your deck! And it's a great way to get some of those Shuriken back! Cards like Alchemist or Larzos which get Items back from the Break Zone can also be helpful here. You can be sure to have lots of Items in the Break Zone when you're playing with Shuriken!
Having another Weapon hanging around may also be useful. It would allow you to throw your last Shuriken without worrying about Yuffie (4) losing all of her nice abilities!
Ninja is also one of the better supported Jobs, with cards like Edge (4), Godo (1) and a host of others giving extra power, ablities, etc. Since there are also a LOT of [Card Name (Ninja)], you could produce some nice synergies.
The weakness here would, of course, be effects which Break items. Since Shuriken doesn't have a Remove cost, you'll be forced to used them, so you don't just lose them. And Yuffie (4) is pretty weak for a cost 5 Forward if she doesn't have her abilities.