One common theme is growth. They both grow as individuals and as a pair. For example, Hinata might help Tsukishima become more open - minded, and Tsukishima could teach Hinata to be more strategic.
Tsukishima's back story has a lot to do with family influence. His brother's success in volleyball was a big factor. He was in his brother's shadow for a long time. As a result, he was hesitant about volleyball. But as he grew in the Karasuno team, he started to find his own identity in the sport, separate from his brother.
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.