Osafune Yoshikage is as important to the sword world as Monet or Van Gogh are to art.

There are 44 Yoshikage Juyo. 15 are Naginata-Naoshi, like this piece. 
In   Jo polish
      Jo Habaki
     Tanobei Saya-gaki
     Tokubetsu Hozon from NBTHK 

This is a first class sword by a first class smith. It is a Juyo Candidate. Solid in the hand, thick and healthy. Dragon Horimono by Yoshikage on both sides.
The NBTHK TokuHozon Kantei is specific to Osafune Yoshikage (not a school attribution of "Den") 

Nagasa: One Shaku four Sun, six Bu  

One of the most important Namboku smiths
See Osafune main-line master, Yoshikage in the following Kanemitsu and Chogi School, Soden Links

 Chogi School
 Kanemitsu School
 Yoshikage info

- NENGO Chrono
- NENGO Alpha