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joining (a group); becoming a member (of); joining the ranks (of)
チームに仲間入りした。
I joined the team.
新しいメンバーが仲間入りして活気が出た。
A new member joined the group and brought new energy.
スポーツ界に新しい才能が仲間入りすることで競争が高まる。
New talent joining the world of sports raises the level of competition.