Osamu is a supporting character in the anime ERASED who appears during the 1988 elementary school timeline as one of Satoru Fujinuma's classmates. He is a young schoolboy with short black hair cut to about ear length and dark eyes. His name, written with a character meaning discipline or study, is one of the few personal details the story highlights about him.

Within the friend group that includes Satoru, Kenya Kobayashi, Hiromi Sugita, and Kazu, Osamu is presented as an ordinary and easygoing child. His most prominent personal trait is his enthusiasm for the video game Dragon Quest, which is mentioned in the early episodes. His home life and individual goals are not expanded upon, and he functions primarily as a background friend rather than a central figure in the drama.

His motivations are not deeply explored. He behaves like a typical boy of his age who enjoys spending time with his companions. His most defining narrative trait is that, among Satoru's friends, he is the only one who does not take part in the efforts to prevent the kidnappings. While the others become involved in watching over Kayo and investigating the threat in their town, Osamu remains uninvolved, which makes his role in the crisis notable mainly for his absence from it.

In terms of relationships, he is closest to Kazu, who is described as his best friend, and he shares a friendly connection with Satoru and the rest of their circle. He does not undergo significant personal development over the course of the story, and he has no special abilities or skills; he is distinguished only by his hobby and by his lack of participation in the central characters' plans. His presence adds texture to the childhood setting, but his importance to the overall story remains minor.