is an ōdachi (Japanese huge greatsword) forged by the swordsmith and an Important Cultural Property of Japan.
The name came from a legend that one night flaws on the blade were repaired by fireflies. The is also known as since it was kept as a treasure of the Aso Shrine.
The was designated an Important Cultural Property of Japan (then-National Treasure) on December 14, 1931.[1] Since the end of World War II, however, it has been missing.
In 2015, Touken Ranbu fans raised 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.[2]