The ending of the Haikyu manga sees the main characters having accomplished their goals and leaving a lasting impact on the volleyball world. It wraps up their stories in a satisfying way.
One popular 'haikyu fanfiction' story could be those that focus on the character development of Hinata outside of the regular matches. For example, some fanfictions might explore his life at home, his relationships with his family members, and how that impacts his growth as a volleyball player. Another type could be the ones that create alternate universes where the teams have different dynamics or face different challenges in the volleyball world. There are also fanfictions that center around the friendships between the characters, like Kageyama and Hinata's evolving bond in new and unexpected scenarios.