Ikutachi the Living Blade/Origin

According to Japanese mythology, Ikutachi was a blade imbued with life and one of the three magical treasures of Ne-no-Kuni (a sort of underworld ruled by Susanoo). The sword was held by Susanoo, then later stolen by Okuninushi along with the other two treasures: the Ikuyumiya bow and arrow, and the Ame-no-Norigoto musical instrument.

Okuninushi (originally known as Onamuchi) fled to Ne-no-Kuni after being killed twice over by his siblings, the Yasogami. While there, he fell in love with Susanoo's daughter, Suberime, and was subjected to a series of harsh trials (such as sleeping in a room of snakes and other creepy-crawlies). With the use of magic and the help of Suberime, Okuninushi passed all the tests and managed to escape with Suberime and the three treasures of Ne-no-Kuni while Susanoo was asleep. When Susanoo woke, he called out to Okuninushi to take revenge on the Yasogami using the weapons he stole. Okuninushi eventually drove out the evil Yasogami and became the great ruler of the terrestrial land.