Joining a group; becoming a member or being accepted into a set of peers.
新人が今日から仲間入りして、一緒にプロジェクトを進めることになった。
A newcomer joined today and will work with us on the project.
子猫が兄弟たちの仲間入りをして、すぐに遊び始めた。
The kitten joined the other siblings and started playing right away.
彼女は正式にチームの仲間入りを果たした。
She officially became a member of the team.