Hotarumaru (蛍丸, "Firefly"[1]) is an ōdachi (Japanese huge greatsword) forged by the swordsmith Rai Kunitoshi (来国俊)[2] and an Important Cultural Property of Japan.[3]
The name came from a legend that one night flaws on the blade were repaired by fireflies.[4][5] The ōdachi is also known as Aso no Hotarumaru (阿蘇の蛍丸) since it was kept as a treasure of the Aso Shrine.[6]
The ōdachi was designated an Important Cultural Property of Japan (then-National Treasure) on December 14, 1931.[3] Since the end of World War II, however, it has been missing.[6]
In 2015, Touken Ranbu fans raised ¥45 million through crowdfunding to construct a replica of the Hotarumaru. During the reconstruction, the Aso Shrine was destroyed from an earthquake in April 2016. A ceremony for the completion of the replica was held on August 27, 2016, and it is now displayed at the Aso Shrine.[7]