Kira no Ken

In the IDW continuity, the Kira no Ken is a legendary sword dating back several centuries, to the period when Kublai Khan attempted to invade Japan. According to legend, a man made a bargain with the gods for the sword, on the condition that it be returned when the Mongol Horde had been defeated. Since it was not returned, it was considered cursed and destroyed every person who wielded it.

At some point during the Muromachi period, it was obtained by Takeshi Tatsuo, who placed it with other valuables that he had collected in a hidden vault guarded by supernatural obstacles. That sword was found again by Oroku Karai many centuries later; she used it when she attacked the stronghold of Hayashi Toru, slicing through a thick steel door with ease before beheading him.