The short answer
Japanese keywords need more than translation. Reflecting script variation across kanji, katakana, hiragana, and romaji — plus real search intent — improves both visibility and conversion.
The same meaning has varied spellings in Japanese. Loanwords, for example, mix katakana and English, so map all variants as keywords.
Classify search intent. Separate informational, comparison, and purchase queries, and place content and landing pages to match intent.
Native review is essential. Awkward literal translation lowers trust and raises risk on regulated expressions such as efficacy guarantees.