Okay, my reading of ni-to-kenjitsu looks like you get to make an attack with the primary weapon AND a parry with the second? I think that means you roll the parry (p.62). If you fail the roll, you still get a +1 AC. You only get no benefit on a critical failure. But on a success on the parry check you get effect/5 to armor class and then an extra +1 if its a critical success?
So you should roll the Parry?
Now, you only get a +2 if your effect number rounds up to 10, so 8 or higher. Your base BCS is 11. So, on a 1 it is critical and +3, on 2-3 it is +2 and on 4-19, it is +1 AC. I suppose that's slim.
Do normal attack modifiers apply to Parry BCS (which is kind of an attack)? If parrying someone who has the wrong facing, or has a height disadvantage, or whatever? That could really improve the effect number.