Izumo is a chuunin from the Leaf Village who's basically inseparable from his partner Kotetsu Hagane. The two first show up trying to talk the genins out of entering the chuunin exams—a job that doesn't exactly work out. Turns out they were actually proctors for the exams the whole time.
After the exams wrap up, the Fifth Hokage recruits them both as assistants and assigns them to guard the village's main gate, a gig they stick with pretty consistently. Fans often note how rarely you see one without the other, and the pair continues showing up throughout Shippuden as well.
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