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overserious; deeply sincere; very earnest
彼の生真面目な性格が時に周囲を疲れさせる。
His overly serious personality sometimes tires those around him.
生真面目すぎて冗談が通じないことがある。
He is so earnest that sometimes jokes don't get through to him.
彼女は生真面目に全ての規則を守っている。
She earnestly follows all the rules.