Rivkin

I think the sugata is ok and the hi appear to be well cut, so there is a chance its real. A detailed shot showing work somewhere on the blade can reveal more.

Late Muromachi (short nakago, yasurime is basically straight, not sugu boshi, sugata etc.), hard to come up with school as polish is very heavy on hadori and sugu-notare hamon is not too distinctive. I would say Mino since later generations did do wide sugu-notare, though I can't see masame in shinogi-ji so might be someone provincial instead.

Late shinshinto to Showa.

Well, it looks late, maybe shinto, a decent blade, more precisely is very hard to say... Owari etc., whatever, many possibilities.

It feels more like a plaque commemorating the war rather than single specific event. Nice Americana but sword has to be judged separately

As always discussion moves towards irrelevant things. Are there Heian Naminohira - if you believe Edo period's publications the answer is yes. If you believe in comparing to blades for which the dating is somewhat known, then the question is whether the early Naminohira appears more ancient compared to Bungo Yukihira. My personal impression is they appear to be of roughly similar age, and Yukihira is known as early Kamakura smith, so its unlikely Naminohira is older by 200 years. The question for this blade is whether it has appearance similar to the earliest Naminohira, and the answer is difficult. The overall shape appears somewhat different, kissaki proportions are a bit different as well, especially taking into account its a relatively wide blade... Maybe there is mizukage or yaki-otoshi or something else. We don't know and its all very theoretical.

Don't know where it goes, but: ko versus sue are specifically introduced to avoid any controversy related to when the school first appeared. There is no certainty in regards to what is the earliest Naminohira blade (there is a dated example but...), and in principle only Senjuin (Mogusa?) and Sanjo (and related) schools more or less certainly were present in the Heian period, the rest borders between "likely" and "not likely". Nishu's sayagaki are seldom associated with the top blades, though there are some. Dr. Honma has been the golden standard and I have not seen a sayagaki of his that has been challenged. That's been the status from the beginning, and he is the founder of the modern sword appraisal and mofrtn understanding of smith's genealogies. Kanzan Sato wrote a lot of sayagaki and I would estimate 5-10% of those have been successfully challenged in modern papers, especially those written in 1974-1976 (by memory). There are various explanations, some say they are faked often (and they are), but then in most cases they are also green papers issued by the head office with the same judgement. Honami Nishu was considered third choice compared to these two gentlemen and the last option for those not satisfied with other opinions. I probably have two dozen photographs of his writing with the NBTHK differing greatly. Lots of Ichimonji classified into Ishido, Hosho into Sendai etc. With each blade I've seen NBTHK position was easy to understand.

Let's stop that. Not helpful and scratches the blade. Potentially Mihara, early Muromachi. To say more one needs pictures of the blade which actually show some activity, not blend reflections.

Hard to be certain especially on a phone, but the shape leans towards pre 1500 and the school is likely Yamato. Even more speculative it’s either 1430 Mihara or 1300 Senuin. In either case likely a good sword

Mino style, boshi is not sugu, very straight with large kissaki - generally hints towards shinshinto, Tensho or Nambokucho. The style is a bit too much Mino to be early, so either Tensho or someone in shinshinto who worked in a traditional Mino style, alike to 10th generation Aizu Kanesada. My personal guess would be the end of Muromachi, sue Seki as the most likely attribution. P.S. The restoration was a bit untraditional.

hmm, I have one for sale... Generally these are of interest to collectors who like to research and study unusual and potentially old forms. They are not common, but such collectors do own quite a few.

The shape is common in some traditions depicting "ancient" daggers. 19th century influence.

Nice blade, late Muromachi, but otherwise it starts to get weird. Could be Bizen, but mitsumune and nakago are uncommon for the school. Looks very much like Mihara, but again mitsumune is not common. On the other hand, tensho period's Odawara did work in suguha a lot, can be a good match.

My answer would be "its extremely complicated". Even discarding the impact of polish, which however is quite large when it comes to nioiguchi, nioiguchi physically demonstrates the temperature gradient due to heat conduction between the portion of steel that is cooled directly by water and the portion which is cooled slowly through clay. So theoretically a very clean steel will give you a tight and bright nioiguchi while slag will create something hazy and uneven. But its not exactly true. First, the forging comes into play as heat conduction within lamination is always higher than between laminations - so if the blade is itame you can have tight and bright nioiguchi (Yamashiro), if it has mokume or masame going in and out hamon nioiguchi there is good chance is not going to be as well defined. Second, daito has quite a lot of material at habuchi level and thus will cool down slower compared to tanto. So tanto with all conditions even will have different (and often brighter) nioiguchi compared to daito, and daito with niku will have broader nioguchi compared to something thin, and if there is a core iron which has some other thermal resistance (usually it does), then two piece sword will have tighter and brighter nioguchi compared to a single piece work... By the same token controlling hardening is usually easier for tanto and for the same amount of nie on daito the margin for error is considerebly smaller.

Nioguchi is not a factor for Hosho. Best Hosho has a lot of chikei, hamon which has strong and bright nie formation, hada with very bright jinie, both masame and itame. Its not as uniform as Sendai or some shinshinto blades, but the non-uniformity adds character, its not awkward or artificial.

Just one: do not read Facts and Fundamentals. He has his system which is based on very obscure things... It works for some blades, but not for others. Lots of Hasebe and Masamune will not have a "quality nioiguchi", in fact it can be quite difficult to observe. There are some Yamashiro and Bizen blades which can be judged by nioiguchi but even then Hizen's very wide nioguchi is not a sign of issues anymore than very tight nioguchi... Brightness counts more, though again his school insists that if its too bright then its acid etched etc. etc. Hosho is very good, as are some Kiyondo and even some Kunikane.

1. The title is wrong. 2. The blade definitely looks like Muromachi Bizen. 3. It seems to be dated/signed but without really large photos its hard to verify the authenticity and frankly its a bit of a bother. So yes, its authentic Muromachi Bizen, the signature could be right could be not, these things are surprisingly often faked. 3800$ is a lot. You can buy decent muromachi daito with mounts for 4000 today.

It depends on the budget. In the best case the strategy is to simply walkin to Sokendo shop, give an attendant a list of what you want to see, tell him you have a budget ready and ask if Kurokawa san can show you the blades. He has an encyclopedic collection so you will see a really good Unshu if you want. Basically if you are in Japan and comfortable buying there (no returns, in most cases incomplete disclosures and some chance of outright lies), you should buy there. If you want moneyback or some other conditions, US is an option, but aside from sword shows its going to be more expensive.

Swords are bad investments. Dealers will tell you otherwise. Unju is a good school, if anything its undervalued. However with the current yen rate 6 million yen is a lot of money for Unju Juyo. They are not terribly uncommon. The mounts are authentic but very late (the very end of Edo, less likely Meiji) with a generic 3-5 pawlonia which is quite common, of good quality. Here is 3 mil yen one: https://sword-auction.com/en/product/14907/as22336-刀無銘（雲次）第22回重要刀剣/ Generally 6 mil at a discount shop buys you decent Ichimonji Juyo or really good Aoe, but then at a premier store you might find the same blade for 12 mil, so its all relative.

Hard to be certain but it appears to be late Muromachi piece. Can be Bizen, so "Bizen Sukesada" attribution is a possibility.

I don't know but I can theorize. Its not satsuma suriage but in shinshinto all foreign and weird things were quite popular. Often the problem dealing with local Japanese experts is they want copies of European hussar blades, smallswords, turkish sabers etc. etc. to date from Momoyama and be connected to one of the famous Daimyo, why in reality the vast majority of such copies were made in 1800s. And many are not copies but actual foreign objects. P.S. And maybe its some rare ikebana ninja sword for cutting lotus flowers I just don't know much about.

Unfortunately even without seeing any activity I would not be optimistic. Sugata is awkward, yasurime is deep and well spaced, patination highly uneven, the kanji are poorly written. Its quite recent (probably post Edo) and the quality I would expect to be on a low side. Even shirasaya is weird with its squarish shape which is probably a bit easier to make.

As little can be seen and earlier Tegai being an option, I personally would still vote for sue-Tegai of Muromachi period. The activity is complex and roundish swirls of ko nie are not that common in early blades but are more typical for Muromachi.

Its unlikely to be kodachi and I would abstain from purchasing this blade. Muromachi period most likely, saiha is a possibility, nothing too exciting as it looks. Ko dachi look deeply curved only when drawn on the same page as regular contemporaries.

Possible, still can't figure out with such light... not that important, for late blades mune shape is not absolutely crucial.