There are two braille systems in Japan. Kantenji is a system that tries to translate kanji into braille. However, it is almost never used according to people I've spoken to on the subject when I was looking for a similar resource.

Therefore, all you need to do is learn how kana are translated to braille. This system follows the Abugida pattern, where the five vowels (a, i, u, e, o) corresponding to braille characters for a, b, c, d, f from memory, are added onto by the dots representing the consonant that finishes the syllable. Therefore, the dots added onto i for shi, and u for su, are similar. There is, therefore, a pattern.

The easiest way to learn is to copy down the hiragana chart on the Japanese braille wikipedia page according to what a visual hiragana chart would look like. I forget how Hiragana and Katakana are distinguished, but the wikipedia page will have entries on that, as well as for how to add the small tsu above a kana to make it lenghtened etc. I really hope that helps, hit me up in private if you have more questions

Check the resources in World Braille Usage.