Mujin

is a shinobi from Sunagakure and a teammate of Sajin and Mijin.

Naruto's Back: Friends' Tracks
Shortly after Gaara was made Fifth Kazekage, Mujin's team went to join an early Chūnin Exam co-sponsored by Sunagakure and Konohagakure. For the first exam, the teams were all split up to take the written test in separate rooms. Shikamaru Nara as proctor explained that everyone only needs to answer one question on the test but their combined score with their teammates will determine if they pass or fail the exam as they need exactly 100 points to pass. While everyone began to panic on how to pass the test, Sajin contacted Mujin and Mijin with his Sand Characters, telling them which question each should handle.