Originally a tachi, then shortened into an uchigatana.
Was said to belong to Akechi Mitsuhide before being wielded by Yuuki Hideyasu's young son, Matsudaira Naomasa (i.e. Ieyasu's grandson), at the siege of Osaka. After his death, it was sold outside the Tokugawa/Matsudaira clans, but was eventually bought back by the Tokugawa.
His name, Kikkou ("tortoise shell"), refers to the engraving on the tang of a chrysanthemum inside a hexagon, bearing resemblance to a tortoise's shell