"A most interesting and highly important tsuba with ongoing study. This tsuba was in the collection of Kenichi Kokubo. It is illustrated in his books: ZABO TANSEN (1974), page 318 and SHINSEN KINKO MEIKAN (1993) page 13 (right entry).
The signature reads: KAWATSU (family name), CHOSA (short for Chosaemon), TAIRA (clan name), IESADA (no saku?).
Date of Kanei Juninen Kit I Go Gatsu. The 12th year of Kanei is 1635, year of the hog. 5th month, May. Thus the date is: May 1635. In the year 1635 was the first of the SANKIN-KOTAI, a policy of the Tokugawa shogunate during most of the Edo period of Japanese history. The purpose was to strengthen central control over the daimyos (major feudal lords). It required feudal lords, daimyo, to alternate living for a year in their domain and in Edo, the capital. It was made compulsory for the tozama daimyōs in 1635.
It would seem that this tsuba was made for this trip. Opposite the date is inscribed: Shogun Den. The Sho kanji is also read Katsu and is not the proper kanji for the title of Shogun which is: hata, masa ni, with the same kanji gun. This seems to refer to the First Trip to Edo.
This is not the only example of this signature recorded so far. See: The Lundgren Collection of Japanese Metalwork, Christies, London, November 18, 1997. Lot 153 page 53, and illustrated on page 55 center left. The tsuba is dated August 1634, ten months before the one above. It is shakudo, mokko shape and with much the same design as the above one. It sold for 2300 pounds plus charges, or $3,910.00 dollars. It sold with a wood box, but no inscription is mentioned. Where this tsuba is today is unknown. If anyone can tell us about this tsuba we would be very grateful. Much more could be written about these tsuba, but first much more research needs to be done." (Haynes)