One common theme is rivalry. Given their positions as volleyball players, many fanfictions explore how their on - court rivalry can translate into a different kind of relationship off the court.
One popular ushijima x oikawa fanfiction is 'Parallel Lines'. It beautifully explores their relationship in an alternate universe where they meet under different circumstances and gradually develop a deep connection.
In the manga, Hinata doesn't outright beat Kageyama. Their relationship is more about mutual growth and competition rather than one consistently defeating the other. Both characters have their strengths and weaknesses, and the story focuses on their development together on the volleyball court.
Kageyama stays with Karasuno in the manga. His character development and contributions to the team continue without him leaving. The bond he forms with his teammates keeps him committed to the club.
Kageyama and Hinata do not date in the manga. Their focus is on improving their volleyball skills and achieving success on the court. Their bond is more of a strong partnership and mutual respect within the sport.