His name means "earth boy".
Jinenji is a huge half-demon who, with his mother, grow healing herbs. At first, they mistake his mother for a yamanba (mountain witch). The herbs they make were once used to save the life of Kirara, who was poisoned by Naraku.
Kagome and the others find him while passing through a village. Despite his monstrous looks, he is very mild and timid. He is accused of killing some of the villagers, but Inuyasha helps prove his innocense.
Later, Jinenji ends up killing another demon - the one who was responsible for the missing villagers.