Directly using the Japanese package for FREE DOS is the simplest solution. The limitation seems to be that for now it can only support SHIFT-JIS.
The advantage is that it can fit on a single floppy disk.
Using MS-DOS/V5。0 is also a solution. But installation is too troublesome, one disk is not enough.
There is also a package called JAPANDOS。EXE, but I haven't used it before. After unpacking it, there doesn't seem to be any documentation file either.
Lastly, what I think is the best solution (although it doesn't quite meet your requirements) is WIN3。1+RICHWIN
test version (it expired in 1996; changing the system date solves it)
If your machine is good enough (nonsense, if it's good enough then wouldn't installing WIN98 solve it), you can also search for
a DOS/V emulator, which can also be used to display Japanese.
All of these can be found with a Baidu search. On the FREE DOS website, click JAPAN MIRRO and you can slowly look around.
If there haven't been any updates within 1 year, the installation package is only a bit over 800K. It doesn't support EUC; of course, after a year I'm not too sure either.
REM 喜欢DOS,因为它的简单
REM 喜欢OS/2,因为它不再矫饰
REM 喜欢BASIC,因为它并不幼稚
REM 喜欢GNU,因为它杂乱无章