The answer is: "OST song" refers to the song in the OST. OST referred to the original music in movies, TV series, and other film and television works, and the song part was the OST song. According to the search results, some OSTs of movies and television works included some songs, such as the theme song of the TV series OST of " A Thought of Passing Mountains," many of Zhou Shen's OST songs, and Yu Kewei's Top Ten Classic OSTs. Therefore, an OST song referred to the song part of the original music in a film or television work.
The OST lineup for the second season of Celebrating Years had already been announced. Among them, Li Jian sang the theme song " In My Lifetime," Zhou Shen sang the ending song " Excuse me," Liang Long, Liu Duanduan, Zhang Haowei, and Guo Zifan performed the promotional song " Aiya." These songs would bring more musical elements to the second season of " Celebrating Years," adding more emotions and atmosphere to the plot.
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.