Yagyū Renyasai’s Wakizashi: the Story of the “Demon’s Knife”

The “Demon’s Knife”: the legendary wakizashi of Yagyū Renyasai

In the vast panorama of Japanese swords, few blades have managed to evoke an aura of mystery and power like the wakizashi nicknamed “Fūchinkiri Mitsuyo,” also known as “Oni no Hōchō”: the Demon’s Knife. Forged for Yagyū Renyasai, master of the Yagyū Shinkage-ryū school and central figure of the Owari lineage, this blade encloses a fascinating interweaving of art, technique, and legend.

An exceptional warrior

Renyasai, direct grandson of the famous Yagyū Sekishūsai and belonging to an important branch of the Shinkage-ryū school, was both a kenjutsu master and a refined aesthete. Unmarried by choice, he led a life devoted to the way of the sword. In addition to his martial skill, he was also an innovator in the field of weapon fittings, inventor of the Yagyū koshirae, of original tsuba, and respected even as a ceramicist and landscaper.

The birth of the blade

According to tradition, Renyasai commissioned his court smith, Hata Mitsuyo, to make an ideal wakizashi, capable of accompanying him in moments when the long katana was not available — common situations at a daimyō’s court or during official visits.
After six failed attempts, Mitsushiro, on the seventh try, presented an extraordinary blade. To prove its effectiveness, he cut through four stacked fūchin (paperweights, usually made of stone, Editor’s note). Renyasai, finally satisfied, accepted the blade: the Fūchinkiri Mitsuyo was born.

A weapon designed for real combat

The wakizashi, approximately 1 shaku 3 sun 6 bu (41.2 cm or 16.2″) in length, presents an asymmetrical structure: the omote side is in kiriha-zukuri style, the ura side is shinogi-zukuri. The temper line (hamon) is suguha, the hada (steel grain) is a fine itame with numerous nie. The blade is relatively short yet sturdy, with a horimono (engraving) of a ken inside the bohi on the omote side.

The demon’s knife

The nickname “Oni no Hōchō” was not given by chance. A well-known anecdote tells of thieves breaking into Renyasai’s room at night. Awakened suddenly, he grasped the wakizashi and eliminated them all with a single strike each. The episode became legendary in the Owari domain, so much so that the name of the blade quickly spread and replicas were even forged.

A symbol of samurai discipline

In feudal Japan, it was always permitted to wear the wakizashi at the side, unlike the katana, which was often left at the entrance of residences. This gave the wakizashi both great tactical and symbolic value. In daily life, the wakizashi was the true safeguard of a samurai’s life. A common saying expressed the concept:

“The closer the weapon is to the body, the more refined and worthy it must be.”

Yet toward the end of the Edo period, the introduction of training with shinai and the distancing from wakizashi combat techniques made them increasingly rare. Tragic episodes, such as the death of Sakamoto Ryōma, who failed to retrieve his katana in time during an attack in a tavern, demonstrate how dangerous it was to forget the art of kenjutsu with the wakizashi.

A legacy that survives

Today, the figure of Yagyū Renyasai and his “Fūchinkiri Mitsuyo” remain milestones in the history of the Japanese sword. Not only for the technical excellence of the weapon, but for the ideal it embodies: the perfect fusion of discipline, precision, and warrior spirit.