In regards to the theme, the motif is of a double nested Mokko. The theme is described as Henka Gata 変化形. Henka refers to change, variation or transformation. I believe in this case, it refers to a variation in the Mokko shape. This tsuba has Nihon Tosogu Bijutsukan ‘Bunka Shiryô” origami issued by the Nihon Tosogu Bijutsukan (日本刀装具美術館 Japanese Sword Fittings Museum).
It is said that Akao tsuba were made for Daimyo or nobles only and not for the general samurai, and that the designs were different from the usual work seen in the more popular schools such as Akasaka, Higo and the likes. This tsuba is grand and majestic in all ways and would be suitable only on a very large sword,
There is a similar tsuba described in the book Tôban Shinpin Zukan ( page 119 ). The description notes it as being ‘old’ and is very well forged and of excellent quality.
The iron on this tsuba is soft and has a lustrous appearance. It is unlike many later Edo period iron guards I have seen before and has the look of the early Higo wrks from the Nishigaki and Jingo masters. The earliest of the Akao masters worked in Echizen and almost exclusively in iron before moving to Kyoto and becoming masters of soft metal works.
The Origami translates as follows.
Dai 16020 Go ( number 16020)
Henka Gata Sukashi Tsuba .Henka means variation or change. In this case I believe it referes to
the double nested mokko shapes or, ‘a variation of Mokko’
Mumei, Akao (unsigned, Akao school)
Mokko Gata, Testsu ji Sukashi Bori.( Mokko shape, Carved Iron Ji Sukashi )
Edo Jidai (Edo period)
Migi o Bunka Shiryo Tosogu to Nintei Suru (the object has to the right is declared culturally important)
Heisei Junen Nigatsu Nijuhachinichi (February 28, 1998)
Nihon Tosogu Bijutsukan (Japanese sword fittings museum) Kancho (museum director) Ikeda Suematsu