As the Afterword indicates, this is a collection of odds and ends in addition to the titular story. I'm guessing that the primary criterion for inclusion was the shounen demographic, as otherwise they're all over the place thematically... unless we consider angst to be the theme here, vaguely. (Okay, that's a bit too vague.) However, the high quality of the individual stories makes this collection a must-read if you're a fan of Shimura-sensei's work.