That rifle is interesting, and I have never seen one before. It appears to be a combination of old parts and newly made crude parts. The bolt handle seems to indicate an earlier bolt, and the stock is decent, better than the barrel or bands. The Germans did much the same thing, factories throwing together previously rejected and trash heap parts with new production. The ejector/bolt stop is neat; crude, but probably effective.
I have no idea what the Japanese symbol means, but just a thought that the term "response" could mean response to an emergency (US invasion) so the "emergency" translation could be accurate enough. I don't think the meaning would be "use only in an emergency it might blow up" but more likely "our response to a national emergency". All of that is, of course, purest supposition.
Jim