I guess japanese

Formwise i would have thought rather japanese but the stamps look chinese?

These type of stamps and the kanji on them originate in China and are Chinese characters but you do find them on some Japanese pottery and, in the area of interest that I have, on the wooden boxes that often come with Japanese studio pottery.

The type of brush decoration reminds me of Japanese Karatsu ware and the shape of the vase also looks Japanese.

However, to be honest I have no idea if it was made in China or Japan and it is an unusual item to find its way to the West.

If Chinese, then I think it is harking back to an early peasant style but looks mid 20th century. Perhaps that is most likely because if it was Japanese I would expect it to have more of a "studio" look than your vase does.