Attack on Titan author Hajime Isayama was actually the one who suggested all of the changes that were made to the characters and story, because "When I [Isayama] read the first draft, it still incorporated elements of the source material. But I [Isayama] felt like the creative aspect was missing, so I [Isayama] suggested that it would be better to remove those elements".
During the sequel production with the Director intended a classic music for a scene, This Second Movie is a Tribute to the song "The End of the World" By Skeeter Davis, Hence it's title "Attack on Titan: The End of the World"
Based on the Anime/Manga of the same name
The shortest part out of the two.