The short answer
Japan SEO is led by Google, but Yahoo Japan can't be ignored. The key is localization that reflects Japanese search intent and script variation — not translation.
Japanese mixes kanji, hiragana, katakana, and romaji, so the same meaning has varied search spellings. Keyword mapping that includes these variants is the starting point for SEO.
Google and Yahoo Japan return similar results but differ in audience and inventory. Design content to Google's standard while accounting for Yahoo traffic.
From an E-E-A-T view, native Japanese review and trust signals (company info, sources, update dates) matter. Design clear question-answer structure for generative answer engines (GEO) too.