Previous answer is
Nagasone Okisato Nyudo Kotetsu
Dated: Kanbun 5, Shimotsuki (October),
Tested by Yamano Kanjurō Hisahide (kaō), cut through two kuruma-gari twice.
長曽祢興里入道虎徹
寬文五年極月十月　山野勘十郎久英(花押)両車雁両度切落

Features: Nagasone Kotetsu Okisato was originally active as an armor maker in Omi or Echizen, but it is said that around 1656 (Meireki 2), when he was about 50 years old, he moved to Edo and became a swordsmith.
He was renowned for the sharpness of his blades, and in the 1797 publication Kaiho Kenjaku, which documented test cutting results of various swords, his works were designated as Saijo O Wazamono (top rank for cutting ability).
His popularity was high even in his time, and his swords were favored by high-ranking officials of the Shogunate, resulting in many forgeries being made.
Originally signed with the kanji “虎徹” (Kotetsu), he began using the character “乕” around Kanbun 4 (1664).
The cutting test inscription on this sword dates to Kanbun 5 (1665), suggesting that the sword was likely produced around the same period.

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Appraisal Quiz #843 (April 19th, 2025)
Who made this sword do you think ?
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Blade Length: 74.24 cm (29.23 in)
Curvature: 1.61 cm (0.63 in)
Mekugi Hole: 1
Width at Base (Motohaba): 3.05 cm (1.20 in)
Width at Tip (Sakihaba): 2.16 cm (0.85 in)
Thickness of rim (Kasane): 0.76 cm (0.30 in)
Sword Weight: 800 grams
Shape:This piece has a wide body, thick kasane, a relatively deep curvature, and a slightly extended, robust kissaki (tip).
Jigane:Well-forged ko-itame hada, forming a refined jigane, known as sometimes referred to as konuka-hada.
Hamon:Nie-based, gunome-midare style. The nioikuchi is deep and rich in nie, making this a masterpiece regarded as an excellent example

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