Oyasumi !

おやすみ !
Oyasumi is another easily remembered phrase, since people usually only use it at night.
Its direct translation to English is "Good night!". However, people usually says Oyasumi nasai / おやすみなさい , since Oyasumi nasai is more formal compared to Oyasumi. Same thing between Ohayou and Oyasumi, both are informal and only used between close friend or family member.

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