I try not forget :P. Unseen Strike is same as 'sneak attack' basically but named differently and it only comes once during class career (which is weird, could imagine 2d6 or 3d6 for shinobi swordsman). Anyways not home so cannot check jutsus so best what I could was use speed rank 2 and then open with normal attack to measure foe's ability without revealing aces yet.