I’d love to see one as well. In anything above the free tier, Grammarly actually provided a style guide and automated editorial oversight rather than actual grammar.
For example, when I was at Uni, Strunk and White’s Elements of Style was the one you were expected to follow when submitting written work. I don’t know what the Japanese analogue to that would be, but hopefully someone can provide some insight.
The only thing I found Grammarly-like for Japanese is 文法-CHECK (ぶんぽう).
Extrapolated from the website: “文法ーCHECK lets you check your Japanese sentences for grammatical errors using an AI model. Just type in the box, hit チェック and any errors will be underlined in red. Really short sentences and the ends of really long sentences won’t be checked, so watch out. Please note this is still an experimental service and results may not always be accurate.”
I don’t remember where I found this, it may be from this very forum or from the Bunpro’s one or Reddit or completely something else.