Van

I would agree to 剛. There are some references to an army veterinarian with this name.

It's numbers and syllables, first picture is the correct way to look at it. 一一一一 1111 タ サ Ta Sa 一0 10

實井 read Jitsui or Sanei. It is a surname. Looks like there was at least one more kanji below that, but it is worn out.

My guess the mysterious kanji is 恆. Which is a variant of 恒, as Tanto54 suggested above. My reference books do not list any 恒祥 though.

Thank you Mr. Volker. There is another seal on top of the inscription, too. Can I see that?

Thank you Mr. Volker for the good resolution. The bottom seal is much worn out, I can distinguish only 1 top-right character and a part of top-left. There's 4 characters there. Maybe a top seal close-up could also be uploaded?

Thank you for the correction.

Maybe you can do a hi-resolution of the inside, too? A close-up on the red seals would be nice, maybe they are readable as well.

I see. Thank you for your patience.

The main contents: Wakizashi Mumei [unsigned], (Fujiwara Takada). Length: 1 shaku 8 sun 3 bu [=about 41.8 cm]. NBTHK certificate dated May 13, 1973 The smaller BoE registration paper adds that sori is 1.3 No much other factual information. P.S. There's some more info like measurements, blade description and some info on the smith on the site where it is sold https://www.aoijapan.jp/脇差無銘藤原高田/

Yes, I know how to enlarge it. I'm asking about your ability to read even this low resolution. I mean I can guess some parts of it even as it was. But small pieces that you cannot guess by logic, like the first kanji in the name? How can you be sure about it? Again, it's not that I doubt. I admire your effort and wish I could learn to do that because I often get low-res puzzles for reading.

Sorry for a stupid question, but how could you read it with this resolution? I don't doubt your reading, but asking about the technical side of the possibility to read. Maybe I do something wrong and it shows too small on my screen?

Maybe it's just me, but the pictures seem too small to read? The inside inscription is a little more visible. 陸軍(主計?)大尉　窪田？夫留魂刀 A blade containing the spirit of Kubota Something-o, captain something of the Army. Cannot be sure with this picture quality. The seals are not readable. Pictures in bigger resolution would be helpful to read it in full.

Numbers in red on the second sword resemble GHQ marks I've seen before, but I'm not a specialist in that field. Maybe somebody can say something more certain about these?

Thank you for clarification.