The Koryû Kagemitsu is a magnificent Japanese tachi sword now held in the Tokyo National Museum. The Koryû was crafted in 1322 by master swordsmith Osafune Kagemitsu of the Osafune school of swordsmiths originally founded in Osafune town, Bizen province by Osafune Mitsutada in the mid Kamakura Era. Even among the Osafune school, which included such famous smiths as Nagamitsu, Kanemitsu, and founder Mitsutada himself, Kagemitsu's swords have the densest steel structure and display the keenest and clearest blade surface, recognizable by the distinctive misty reflection line (midare utsuri) in the grain.
The Koryû draws it's name from the relief of a small dragon ("koruyû") coiling itself around a blade, found on the lower front groove of the sword (the outer side of the blade when hung with the cutting edge downward in proper tachi style). A Sanskrit character on the back side of the blade suggests that the dragon represents Fudô (Sanskrit Acalanatha), the King of Light in Esoteric Buddhism. At some point, the sword was slightly shortened by cutting part of the tang, such that now the dragon would be partly hidden when a hilt is attached. Thus the sword has sometimes been called the Nozoki ("peeking") Kagemitsu, since the dragon appears to be peeking out from under the hilt.
The Koryû Kagemitsu was presented to Emperor Meiji in 1873 by its then owner Yamada Yoshitoshi through Okubo Ichio, the then governor of Tokyo, whence it made its way to the National Museum, and has tentatively been traced back to the famous samurai Kusunoki Masashige. The Koryû Kagemitsu is one of the finest examples of Japanese swordcraft, and was designated a National Treasure in 1952.