The "Dragonfly—Cutter" is a famed spear created by Fujiwara Masazane of the Mikawa—Monju school, whose founder, Muramasa, moved to Mikawa after falling out with his previous benefactors the Tokugawa family. Known as the preferred weapon of Honda Tadakatsu, and one of the three greatest spears in Japanese history.
Its name comes from a famed incident where a dragonfly ("tombo") unwittingly flew into the spear's blade and cut itself in two.
At the time, many lords took the dragonfly as a symbol for its habit of always flying forwards, but never backwards. The image of a dragonfly sliced in two by simple contact with the spear lends credence to the legend that its sharp blade cut down many a warrior in its day.