It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
The theme song might not be the opening song. Although the theme song usually referred to the opening song, sometimes the theme song could be other songs instead of the opening song. Therefore, the theme song and the opening song could be defined and used differently in a work.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
It could mean that a person who is a fan of 'Attack on Titan' (AOT) is reading or watching fan - created fictional works related to AOT. Maybe they are interested in seeing different interpretations or storylines that fans have come up with.
One way is to check on popular fanfiction websites. Look for ones with high ratings and a lot of reviews. For example, Archive of Our Own (AO3) has a large collection of AOT fanfictions. You can search for the most popular ones there.
The opening theme song of " Celebrating Years " was " Years " sung by Xiao Zhan. This song was composed by Duan Sisi, composed by Tan Xuan, and arranged by Chen Sitong. It was included in the album "Years" and was released on December 28, 2019.
" Celebrating Years " was a popular historical novel. The author was Maoni. It was published on Qidian Chinese website and was widely loved by readers. The story described how Fan Xian fell into a huge conspiracy when he transmigrated. The book described how he solved the mystery step by step. You can read or listen to this book on the Qidian Reading App. You can also get an experience member by going to Qidian Reading App. You can read the original book and listen to the original audio on the Qidian Reading App. The male lead, Fan Xian, was a person who valued relationships and righteousness, had a bit of humor, and had very upright values. His martial arts were strong. The female lead, Lin Wan 'er, was innocent and knowledgeable. She was a typical lady.