This article explores the historical development of the Japanese language and discusses which languages are most closely related to it today. It looks at the unique features of these languages, such as grammar, vocabulary, and pronunciation, and compares them to the Japanese language. It is revealed that Korean, Ryukyuan Languages, and Ainu Language are all considered close relatives or "sister" languages due to their shared history or similar grammar structures. Understanding these similarities can help us gain insight into how these related languages differ and evolve over time.