The manga is a relatively original story that looks simple but holds quite a bunch of subtleties and notes of philosophy, which seems to have become the mangaka's trademark. For a 1-volume work I'm actually impressed with how the characters progressed given the limited amount of space and time. There's a certain level of drama - even if faint, and even action, but ultimately this manga is mainly all about the different journeys that the characters take, from the past, present to the unforeseeable future, with each stage showing how character growth has taken place since the last one.