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the head; the foremost; beginning; the very front
困ったときに真っ先に相談するのはいつも彼だ。
He's always the first person I consult when I'm in trouble.
彼女は真っ先に手を挙げて質問に答えた様子だ。
She seemed to raise her hand first and answer the question.
新製品が出たら真っ先に買いたいと思っている。
I want to be the first to buy new products when they come out.