Hi Luca
Generally you have the Shoami school and the variations like, Aizu Shoami, Iyo Shoami etc
The variations have a distinctive style and your is not from one of these style.
It may be Kyo Shoami (somewhere to start looking) and they can be a similar size, circa 1700 but the side opening (hitsuana) is more of a 'squashed' shape than yours
The correct colour never comes out well in images which is a shame
It has been remounted a few times which is always a good sign
Hopefully someone more of experience will add their input.