Yashaken was a katana said to be crafted by master swordsmith Masamune. The sword was made of triple-forged steel with a helm-guard carved with a ki-rin and believed to be enchanted, undefeatable in battle while wielded. The sword found its way into the hands of samurai called Nishimori in the 1630s. Following a series of battles, Nishimori became disillusioned with his shogun when ordered to execute 35,000 prisoners.