You cannot prove the absence of ninjas, only their direct presence.   For years, the enemies of Mr. Lo and the Triple Union Society died under mysterious circumstances, due to the ministrations of the silent assassins trained in the ninja arts of ancient Sihai and the mysterious world of Yokai Blossom. Trained in the arts of poison, stealth, and the silent blade, ninjas were a key weapon in Mr. Lo's arsenal. Silent, deadly, and fanatically loyal, you never know when ninjas might be lurking in the shadows...