What is written on this grave

If the Japanese symbol on the grave is present in both languages, it is not fair to say that those who are fluent in Chinese have no knowledge of Japanese, as this is one of many Japanese symbols that they would undoubtedly recognize.

I see what you did there. They would have some knowledge, but they do not need to know anything Hiragana or Katakana to know what it means. ie: Not fluent.

My point remains: People who are not fluent in Japanese can read that grave.