Fang, otherwise known as Shishiou, was smithed close to the end of Heian period (794 - 1185) by an unkown blacksmith. However, from the way the tachi is made, historians are able to identify that it was made by a blacksmith from Yamato no Kuni. Shishiou was once owned by Minamoto no Yorimasa and there's a story behind how Minamoto no Yorimasa came to acquire Shishou. This story was written in the Heike Monogatari.
The nobles in the castle then tried to think up of another way to save the emperor. Minamoto no Yorimasa was brought up and they thought that maybe he's the right person to ask for help from. Minamoto no Yorimasa's father, Minamoto no Yorimitsu (源頼光) was after all famous for exterminating a demon and they thought that as his son, Yorimasa might have inherited his father's wisdom and skills to save the emperor.
Minamoto no Yorimasa rushed to the emperor's aid together with his follower, I no Hayata (猪早太) . Once again when 2am approached, dark clouds started to form above the castle. Yorimasa anxiously waited for the weird cries coming from the skies above. Soon, he heard a cry that sounded like a White's thrush. (White's thrush is a bird, 虎鶫 Toratsugumi). Moments later a demon emerged from the dark clouds. The demon had a head of a monkey, the body of a fox, the tail of a snake and the limbs of a tiger. The demon was a Nue (鵺). The nobles were terrified at the sight of the demon, but Yorimasa wasn't faltered by the Nue. As soon as Yorimasa took out his bow the demon hid itself again among the clouds. Luckily enough the Nue still made those screechy cries and Yorimasa pulled his bow and shot an arrow towards the direction those cries were coming from. The arrow managed to hit the Nue and it fell down from the skies and onto the ground. However, an arrow was not enough to kill this demon. Yorimasa's follower, I no Hayata then rushed to the Nue and used his tachi to deal the finishing blow. It was said that he made a total of 9 cuts on the Nue before it finally died.
As soon as the Nue was killed, Konoe Tennou's illness went away almost immediately. The emperor was impressed and he wanted to reward Yorimasa for his great deed. The emperor then presented a tachi named Shishiou (獅子王) to Yorimasa. And that's all for Shishiou's story!