In Japanese mythology, Ame no Sakahoko ("upturned sky-spear") was a hoko or halberd used by the twin gods Izanagi and Izanami to calm the primordial chaos and create the earth. According to some legends, the weapon was later gifted to the god Ninigi-no-Mikoto, who was sent to earth as its ruler. It's said that he stuck it in the stone on the summit of Mount Takachiho, where it still stands today, thinking it was best to hide it so that no one could misuse its powers.

Although there is no account of the actual origin of the bronze halberd on the mountaintop, it has been suggested that it may date to the Nara period (710-794 CE). Likely fearing the mythical powers of the Sakahoko, no one dared to examine or study it for centuries, until Sakamoto Ryōma. 

Ryōma is one of the most famous samurai of 19th-century Japan, often credited as being influential in the restoration of imperial rule, which led to the country's modernization. Despite being a low-ranked samurai, he became one of the most notorious opponents of the Tokugawa shogunate. He also helped found the Satchō Alliance, uniting two rival provinces against the Bakufu (government).

Merely two days after the establishment of the Satchō Alliance, Ryōma was attacked by a group of assailants sent by the Bakufu. He narrowly managed to escape the assassination attempt with only slight injuries, thanks to his wife Oryō's quick thinking. On the recommendation of friends, who were well-informed on Western culture, Ryōma took his wife on a honeymoon trip to the hot springs of Kirishima.

During their honeymoon, Ryōma and Oryō visited several places in Kirishima, including the sacred mountain of Takachiho. Possibly in an attempt to impress his wife, Ryōma pulled the Sakahoko from the summit, as recorded in a letter he later wrote to his sister.

An active volcano, Mount Takachiho erupted in 1913, breaking the Ame no Sakahoko in half. Its blade was gifted to the Shimazu samurai clan, who then dedicated it to a nearby shrine, but it's believed to be lost today. The original handle is still embedded in the summit, and a replica has been placed there anew, although its creator is still unknown.