O-Kanemitsu (Great Kanemitsu), as he is known, represented the mainstream of the Osafune school in Bizen Province following his father, Kagemitsu. His signed work dates from the 1st year of the Genko era in the late Kamakura period to swords made in the Joji era (1362-68) in the Nanbokucho period. His work from the early Nanbokucho period is substantially in the style of Kagemitsu, often with suguha or like this piece, kata-ochi-gunome. But from around the middle of his active period he produced 'o-dachi', long and broad with extended kissaki, and introduced the characteristic notare found on many of his later works.
This blade has the classic Osafune characteristics, and is typical of middle Nanbokucho-period swords. Although o-suriage it retains a deep curve with an element of koshi-zori.
The attribution to Bizen Kanemitsu, or kinpun mei (gold powder inscription) in gold lacquer is given by Hon'ami Koson (1879-1956), of the Maebashi clan of Joshu Province. He was both polisher and sword connoisseur, and published a number of books including Nipponto no okite to tokucho (Rules and characteristics of Japanese swords) at the age of 77, a year before his death.
It is likely that the sword was cut down during the Muromachi period, and although there might have been a known provenance and tradition that it was the work of Kanemitsu, the attribution would have been confidently made by Koson at the time of polishing.