Oyasumi nasai means "Good night." This phrase is used when you are saying goodbye to someone for the night, especially before going to bed. It's a polite and gentle farewell. You can say this to family members or close friends. For example, "もう寝るね。おやすみなさい！" (I'm going to bed now. Good night!).

夜、寝る前に別れるときに使う挨拶です。家族や親しい人に言います。「おやすみなさい。」