Japanese culture has used symbols (not kanji, more like dingbats) for at least 20 years if not 30 to 35. They use them in business documents all the time. The most common are probably ●○◎■□▲△▼△. In fact like in the USA a generic name might be "Smith" in Japanese they often using 〇〇さん.
Further, they've been using emoji for the last 20 years. So telling them they can't is basically telling all of Japan they're 2nd class. Their standards and ways of communicating don't matter. Lots of programmers from cultures where emoji and symbols were not in common use dismiss them because in their culture they were not in common use just a few years ago but other cultures have been using them much much longer. As such, banning them is unintentionally racist.
Further, they've been using emoji for the last 20 years. So telling them they can't is basically telling all of Japan they're 2nd class. Their standards and ways of communicating don't matter. Lots of programmers from cultures where emoji and symbols were not in common use dismiss them because in their culture they were not in common use just a few years ago but other cultures have been using them much much longer. As such, banning them is unintentionally racist.