Originally an Imperial Treasure. Emperor Oogimachi presented it to Ashikaga Yoshiaki, then it went into the hand of Oda Nobunaga and Toyotomi Hideyoshi. It was said that he was named Nihongou during the time he belonged to Hideyoshi. There is also a theory that he was actually a tachi which is so good for thrusting that he ended up getting put as a spearhead. (Source: Touken Ranbu Wiki)