Hamon
According to the Japanese Wikipedia, the hallmark of his manner is the 拳形丁子 (kobushigata-chōji), a chōji with heads rounded like fists. It is the trace that was found in 2015 beneath the straight temper of Ryōma’s katana, and what allowed the blade to be attributed to him.
Nakago and mei
He signed 陸奥守吉行 (Mutsu no Kami Yoshiyuki), or just 吉行 (Yoshiyuki), according to the Japanese Wikipedia. Ryōma’s katana bears 吉行 (Yoshiyuki) on the tang, without a title, and a single hole.
What is not on record
None of the sources consulted describes his sugata, his jihada, his bōshi or the shape of his tang and its file marks. The only blade studied, Ryōma’s, lost its shape and its temper in the fire of 1913.
Who he is confused with
There were other smiths who signed Yoshiyuki: the attribution of Ryōma’s katana to Mutsu no Kami Yoshiyuki is made by the Japanese Wikipedia on the basis of the temper and the family papers; the museum catalogues it only by its signature. The Tokyo National Museum holds another katana signed 吉行 (Yoshiyuki) (F-267), with no description or attribution in its record.
Details
The tang of Ryōma’s katana, reddened by the fire of 1913. Kyoto National Museum, CC BY 4.0, via Wikimedia Commons · CC BY 4.0 · source
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