Romantic subplot, is a term you some may be familiar with. The manga, to me appear to have the sports themes as the sub plot. It seemed like the mangaka was trying to write a romance story line and a sport story line at the same time. As a reader I felt that the "gears" in my reading were going up and down as the story transferred between the romance aspect to the sports aspect of the story line. At one moment you are focused on the main character improving himself and then having another romantic interlude. If i go in depth I would almostsay this a series of romantic one-shots cobbled together through a story about badminton. In some cases in the beginning is seemed almost too much romance and toward the end almost too much sports.
One thing I will never understand is the random appearance of the main character's sister in one page of the manga yet through out the story she is never once mentioned before or after that page. In context it is served as a fan service nothing more. It also feels like the last volume was rushed, even the last chapter, however it was a decent enough ending, quite surprising too considering.