Kojima placed his awakening to reading in fifth grade, when he…

Kojima said that as a child he did not read and that he rejected reading without having tried it. In fifth grade he picked up Murder on the Orient Express because there was a film adaptation and he only wanted to see what the book was like; the novel struck him, sparked his curiosity, and led him to read almost all the Agatha Christie he could find before reaching middle school.

When still a student, Kojima wrote an unpublished novel titled Kodoku no Toh: on Christmas Eve a lonely college student gets drunk at a party in an automated tower near Osaka Station and wakes locked inside by its AI. After failing even by setting a fire to escape, he decides that the food, information, and entertainment of that comfortable isolation might be better than his life outside, until a year later he looks out a window and sees something strange.

According to the Newsweek profile of him in 2001, Kojima wrote in middle school five 600-page science-fiction novels.

In high school, a line from The Moon over the Mountain left Kojima dumbstruck; until then he had boasted of reading only foreign science fiction and mysteries. He reread the story aloud in class, at home, and wherever he could until he memorized it completely; for years he proudly assumed no one else had done the same, until he later learned that the writer Koji Yanagi had also memorized it during his student days.

After Publish or Perish, Kojima began slipping away alone to the bookstore opposite the tutoring school and felt that spending time among the books meant he had entered the adult world. He awaited each monthly Columbo novelization and went to the bookstore weekly even when no new book had come out, to the point of wondering whether he was really attending the tutoring school or the shop. There he discovered Agatha Christie and Ellery Queen, which opened the way to mysteries, science fiction, adventure, and his future profession.