Kikugosaku (菊御作), literally "chrysanthemum-made" or "imperial work," designates those blades produced under the direct personal involvement of retired Emperor Go-Toba (後鳥羽上皇) during the early period. The Emperor is said to have selected the (designated smiths), organized them into rotating duty groups at his cloistered palace, and had them forge swords under his supervision. Among the blades produced by these smiths, those for which the Emperor himself performed the -- the critical hardening of the tempered edge -- are termed or Gosaku. Because the workmanship depended upon which smith served as the Emperor's counterpart at the time, their styles differ markedly: some resemble the manner of Ko-, others show a flavor, and still others approach the working range of . They represent not the output of a single hand but a collaborative imperial undertaking unprecedented in the history of the Japanese sword.
The defining physical hallmark of Kikugosaku blades is the (hairline engraving) chrysanthemum crest -- either sixteen- or twenty-four-petaled -- incised at the base of the . Many examples display -otoshi (a temper that drops off toward the base), and from that area a -like often appears. Those worked in the Ko- idiom tend toward brilliant and flamboyant with and , a -dominant with , and vivid standing out clearly over well-forged with fine adhering densely "in a dustlike manner." Others, closer to the or range, present -based shallow mixed with and , abundant , and and . The is characteristically in feeling, turning in a small manner with only a slight . are typically with , preserving the original form that authenticates the chrysanthemum engraving.
Kikugosaku blades occupy a singular position in the Japanese sword tradition as the only group attributed to imperial participation in the forging process itself. Their rarity is compounded by exceptional provenance: one example, transmitted in the hatamoto Kuroda family, was bestowed by Tokugawa Ieyasu in Keicho 19, with the shogunate's officials traveling annually to the Kuroda residence to maintain it throughout the period. Another, accompanied by a Kotsune valued at 150 , bears beneath its chrysanthemum crest the character "" -- a feature for which "no other comparable case is known," making it "a precious piece of documentary material." Where condition permits full assessment, the and are described as remarkably -- sound and well-preserved -- "to the point that, at first glance, one even senses a freshness." Overall, the judges these works to demonstrate "truly splendid workmanship," affirming their place as monuments of the early forging tradition.