Hidemitsu signed and dated his blades, and the dates run in an unbroken file from the era through Eiwa, Eitoku, Shitoku, Kakei, Kōō, Meitoku and into the years, so that an , signed and dated survives from almost every reign of the late . He is a smith, and the published sources count him, in the words of one entry, among "the group of smiths known as the -", the periphery of late- that the institution defines by exclusion: the makers who do not belong to the Kanemitsu line, nor to Chōgi, Motoshige or the group. One account makes him a son of Motomitsu in the Kanemitsu line. The entries are careful about his generations: the places a first Hidemitsu around the Kenmu era but notes that works of that earliest generation are scarcely seen, then counts the name across some four generations down into Ōei, while warning that strict generation-by-generation differentiation remains a matter for further research. Each surviving blade is therefore read by its style and its date rather than firmly assigned to one hand.
His characteristic work is a small-patterned irregular temper. The published sources put it plainly: his manner is "in the manner of Kanemitsu, yet with still finer and smaller patterning", and the words name the whole tell of his hand. Where the Kanemitsu line tempers a bolder , Hidemitsu reduces the same idea to a small, subdued line, ko-gunome mixed with angular elements, pointed togariba and open-valley gunome, the ashi and yō entering well, the temper nioi-dominant with ko-nie and overall kozumu, that subdued, drawn-in quality the entries return to again and again. The bōshi follows the edge into a midare-komi that points or rounds to a ko-maru. His ko-gunome often runs in a linked, continuous rhythm, and on one tantō the published sources find him aligning the small gunome in the uniform Yoshii-mono manner rather than the Kanemitsu one.
The jigane is the constant. He forges an itame, frequently a well-packed ko-itame mixed with mokume and a flowing tendency, the grain standing a little, with ji-nie laid finely and at times densely, fine chikei sunk within it, and a midare-utsuri rising clearly on his best blades. The published sources read the standing itame, the blackish chikei-like iron and the subdued small gunome as features common to the whole Kosori category rather than personal to him, and they grant that his finest forging is well-refined and of fine quality, bright and clear in both ji and ha. On his tantō and hira-zukuri pieces the reflection takes a different form, a bō-utsuri or a straight utsuri running along the line of the yakigashira.
Two further registers complete the picture. The first is the carving. His tantō carry bō-hi with tsure-hi, suken, futasuji-hi, and devotional motifs of bonji, gomabashi and the gyō no Kurikara; on one Eiwa tantō the published sources observe that the Kurikara preserves the Osafune carving manner running, in their phrase, from the time of Nagamitsu through the Kamakura and Nanbokuchō periods. The second is a quieter temper. A small minority of his blades abandon the midare for a bright, clear chū-suguha, the nioiguchi somewhat deep with slight ko-nie; on one such tachi the suguha mixes in gunome with a reverse-slanting saka-ashi and pale, double-hamon-like nie-suji, and the published sources liken the manner to "that of the neighbouring Aoe school"3, calling the blade "an outstanding example among this smith's works"4. The entries value such pure suguha as documentary material for the working range of the smith and the group.
What sets the Kosori Hidemitsu in his place is exactly what the judges name. He is held apart from the Kanemitsu mainstream by the smaller, more subdued scale of his patterning and the somewhat lower rank the published sources assign the whole Kosori group, and apart from the next age by a single forward-looking detail: on a Meitoku tantō the open-valley gunome he tempers, in the entry's words, "already suggests an anticipation of the Ōei-period Bizen manner"5. He stands, then, on the threshold between the NanbokuchōOsafune mainstream and the Bizen that would flower again in Ōei, a maker through whose dated, signed blades the late history of Osafune can be read year by year.
For the collector he is, above all, a documentary name. Hidemitsu has no National Treasures and no Tokubetsu Jūyō; his record runs through three Important Cultural Properties and sixteen Jūyō blades, almost all of them ubu, signed and dated, which is the source of their value, for an ubuNanbokuchōtachi carrying both signature and a reign date is repeatedly called extremely valuable reference material. The provenance is good: one tachi descended in the Kuroda house with a Hon'ami Kōchū origami of Genroku 13 assessing it at fifteen gold pieces; another was among the personal effects of Tenshin'in, the lawful wife of the thirteenth shogun Tokugawa Iesada, who entered the Tokugawa house from the Takatsukasa family; further blades passed through the Tokugawa, Hōjō and Tani families. Most are held, not traded. Examples in the Jūyō tier do come to light from time to time, more readily than the great mid-KamakuraOsafune names but seldom even so, and a signed, dated Kosori Hidemitsu is a precise and legible document of how the Osafune school closed its Nanbokuchō age.
Historical importance
Where Hidemitsu stands among comparable artisans: across all of nihontō, and within tradition, era, and period. The tiers (Foremost · Leading · Major · Notable) weigh official designations from the NBTHK and Japan's Agency for Cultural Affairs, together with historical honors of lasting repute such as the Sansaku and Meibutsu-chō.