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(young and) innocent; naive; pure; fresh; artless; unsophisticated
新入社員は初々しい笑顔で挨拶した。
The new employee greeted with an innocent smile.
入社したばかりの頃の彼女はとても初々しかった。
She was very fresh and innocent when she had just joined the company.
三年目になると、もう初々しくない。
By the third year, one is no longer fresh-faced.