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That's a stylized rain dragon, common in Kaga zogan pieces

I have one even earlier than Edo period, Tensho koshirae from Muromachi period, still with the original blade inside. All lacquered black, even the original seppa have traces.

Thank you for entrusting me with this restoration, at first it looked quite serious but after removing the oxidation I found that the original patina underneath was pretty much untouched by corrosion, also the zogan was rock solid in position, a testament to the quality of the work from this tsubashi. So I just had to make a new patina on the brass and stabilize the iron patina. It was a pleasure bringing back to life this excellent work.

Small groves are filed to ensure more grip and prevent it to slip towards the center of the nakago ana

Actually it is listed in Sesko's Sworsdmiths book MOTOSHIGE (元重), Genkō (元享, 1321-1324), Mino – “Motoshige” (元重), “Rokurōzaemon no Jō Motoshige” (六郎左衛門尉元重), first name Rokurōzaemon (六郎左衛門), it is said that he moved once from Kyūshū to Yamato to join there the Senju´in school, in the second year of Genkō (1322) he moved to Seki and acted their as one ancestor of the Seki smiths, kiri-yaasurime, no authentic zaimei blades are extant by him, it is also said that he was the same smith as Motoshige (基重) I followed the auction as i thought it's an interesting blade to own, but that's way above my means

I agree with paint, more than lacquer. Patina doesn't flake off. An alternative would be fire scale, but the tsuba doesn't look it's been damaged by fire so that's unlikely.

Sekigane are simply held by friction, many times an inlet is filed on the tsuba to make them hold more firmly, then filed to the exact size of the nakago. The umegane of hitsu ana are cut and filed to the precise size needed to lock in the hole and decorated, then tapped in. Usually they're not a single piece but two thin plates with pitch between them which helps to stick even more.

I tried use a Japanese AI tool, still doesn't make too much sense but maybe can help you fill some blanks

Thank you Steve, very interesting, I'll try dig more on that

During my last trip in Japan I found this nice nozarashi themed painting, but the translation is way too hard for me, can someone be of assistance?

I think i remember seeing that bust at old NBTHK museum, before they moved to the new location, so i think most likely it's in the new museum https://maps.app.goo.gl/NmUZRNhaapaCiXHt7

If anyone of you guys is going DTI this year and wish to say hi and see this tsuba and another one of mine in hand just drop me a message

No, there's no kozuka slot. The saya Is plain with horn koiguchi, kurikata and kaerizuno, kojiri Is missing

Yes, everything is lacquered, there's also traces on the seppa. Probably that's why it preserved so well

Bushū-jū Masatsune (武州住正恒)