
Deadly fingernail weapons, known as neko-te. (A more modern and fashionable version than a 16th century ninja would have had accessed to.)
If you’re a ninja, you might need to blind an enemy (at least temporarily), cross a swamp, or turn your hairpin into a deadly weapon. Check out this website to discover some of the tools you might have used! I haven’t encountered all of these in my research, but they sound at least plausible. And I might have to use the thing about the crickets in a book someday….