Hello,

There were about 14 recorded Nagamitsu signing 長光 (as opposed to the 10 signing 永光, etc.) in history, but this one is quite clearly Ichihara 市原 Nagamitsu who worked as a WWII guntō smith. Even if the very distinctive meibun with the "curly" strokes + two horizontal strokes in the "naga" didn't give that away, before I even compared oshigata (rubbings) the depth of the patina, style of yasurime (filing marks), long triangular tagane (chisel marks), and sharply drilled mekugi-ana made it quite obvious that this is a Shōwa-period sword. Ichihara Nagamitsu worked in Okayama prefecture rather than Seki (Gifu) like most guntō smiths, and was an RJT smith too. Unlike many wartime smiths his blades are often considered gendaitō (lit. "modern swords" but in practice used to mean traditionally-made swords using tamahagane, as opposed to non-traditional guntō).

Please check out my owner's guide for more info on care & handling, photography, authentication / restoration, etc. More photos would certainly be appreciated to judge condition, quality etc.

Cool sword! If it's a real 長光 (typing it in so you can look it up.) one of his pieces is considered a Japanese national treasure. Get it appraised!

Here's /u/gabedamien's guide for taking care of Nihonto.

Please do provide more photos if possible.