Previous answer is
Nagasone Okimasa

Special feature : Nagasone Okimasa was generally called Atsubee
who was a student of Kotetsu and become adopted later on.
Nagasone Okimasa has made swords with Kotetsu. He spent most of his life producing swords of his mentor.
Kotetsu has been making swords for 20 year which is not a long period of time yet there are quite an amount of katana existing.
Therefore it is most likely that Okimasa and other wordsmiths has helped making swords for Kotetsu.
One of the reason that made Kotetsu so famous is because of the sharp and bright ha and fine jigane.
From the deep Nioikuchi, Gunome Midare style, this blade looks like Kotetsu.
This blade is almost Katana size and very sharp(Jojo-saku, Saijo Oowazamono rank).
This is his masterpiece of blade.

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Appraisal Quiz #275 (January 24th, 2014)
Who made this sword do you think ?
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Hints. ※The picture will be enlarged

Blade length : 54.24 cm or 21.35 inches.
Sori : 1.8 cm or 0.70 inches.
Mekugi: 1
Width at the hamachi : 3.02 cm or 1.18 inches.
Width at the Kissaki : 1.8 cm or 0.70 inches.
Kasane : 0.81 cm or 0.31 inches.
Shape : Wide and thick blade. Long Wakizashi.
Jitetsu : Ko-itame hada well grained with Jinie. Oosaka Jigane.
Hamon : Nie deki, Around Hamachi part is Suguha. Deep Nioikuchi Doran Ba.
There are wide Ashi. Boshi is also deep Nioikuchi and round Togari gokoro style.

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