Right out of the woodwork:  a suriage, machi okure, wakizashi with two mekugiana, signed, Nagasone Okimasa.  Shinogizukure, iroi mune, sakizori, chu kissaki. Hawatare:  1 Shaku 9  sun 0 bu 6.9 rin  (57.785 cm. / 22.75").  Motohaba: 3 cm. Sakihaba:  2.1 cm. Kasane:  7 mm.  Gunome midare with togare in fine konie deki, thick creamy habuchi.  Tight itame jigane The boshi is a komaru, with a moderate kaeri.  One piece silver foil habaki.  The blade has no chips or cracks, but has scrathes from an abrasive, and stains, but no red rust.  It definitely needs, and deserves a proper Japanese polish.  Rated Jojo Saku with a sharpness rating of Owazamono, in Nihon Toko Jiten - Shinto Hen, Pictured in Shinto Taikan Vol 2, Nihonto Zuikan - Shinto Vol. Toko Taikan, as shown below, as well as many texts on Japanese swords. 

Black lacquer saya under a leather military cover.  The tsuka has mumei Nara shakudo fuchi-kashira with ferns and grasses in gold and silver in takazogan. There are no menuki, and the tight brown tsuka maki is over fine grained shark skin.

The  tsuba is an octagonal Namban style tsuba. 

Nagasone Okimasa is a legendary student  of Nagasone Okisato (Kotetsu), working around Enpo jidai(1673 - 1681) and is known foe exceptional cutting ability (O-wazamono).  It is believed by many that his works are equal to those of Kotetsu.

The octagonal iron tsuba  7.3 cm x 7.3 cm x 6 mm.  with gold leaf dragons facing each other, and roof tops, on a filigree plate,  Produced in continental Asia, and dapted for Japanese use,  The tsuba is six distinct pieces.  The main body is a black iron with gold, the seppadai is iron, of a different alloy, there are two copper spacers contacting the shakudo hitsuana to the seppadai.  

Comment from James McElhinney:  The maker of this guard appears to have intended it to look exotic; possibly for use by the Dutch VOC as a greeting-gift, or as a flashy curio for foreign consumption in Japan, or elsewhere.

It's mishmash of iconographic elements fall outside the design conventions of Qing hushou or Monsoon Asian sword guards.   The dragon morphology is quasi-Islamic/Monsoon Asian — pointed forelock, smooth body, tiny feet. My guess is that this guard was made in Tonkin / northern Vietnam — an area famed for producing high quality metalwork for the Dutch.  The modifications for Japanese use seem to be the handiwork of a Yagami-trained carver.

This has never been to shinsa, so you will be buying on your judgment.                                                                                               $3,500