These don’t look like the characters that Japanese shares with Mandarin. I guess there’s another set?
At the time, Japanese used three glyph sets: kanji, adapted from Chinese hanzi; and hiragana and katakana, invented locally as shorthand for kanji. The latter are syllabaries (i.e., one symbol per sound in the language) with around 50 glyphs. Nowadays, Japanese uses four glyph sets, since English is often intermixed for titles and headers.
FWIW, 'cause I just can't stop: A lot of "Japanese" culture is "Chinese, circa 10th century" because of its dominance, but the two languages have very different grammar and hanzi were never a complete fit; hiragana are tacked-on for verb conjugations. This print is written with no kanji, probably because it's aimed at a literate but relatively "lowbrow" audience. The fraction of writing that uses kanji has increased in the age of word processors, since people needn't remember how to write complex characters for obscure words. In Ancient Egypt, "hieroglyphic and hieratic" are a similar complex-simple pair, because humans are inherently lazy and rushed.