It's far from my area of expertise, but a couple of possible clues: The buckle looks like it was worked by hand rather than being poured into a mold of some type. The hallmarks look like they were hand-carved from wood. The wabi-sabi aesthetic in Japan prizes a certain rough-hewn workmanship, but that's not the feeling I'm getting from this buckle. The technology for typesetting/printmaking and especially metalwork has been developed to a high degree in Japan since pretty far back, so the buckle and the hallmarks would have seemed really crude 75 or even 150 years ago. This makes me think it's much older.
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