In a new Crunchyroll interview with Attack on Titan author Hajime Isayama, the mangaka said there are “no plans right now” for any spin-offs tied to the series. However, there could still be more coming tied to the series. In a follow up question about Attack on Titan characters and backstories, Isayama mentioned the potential for Levi and said, “I actually have something in my mind.” [Thanks, Crunchyroll!]
With regards to an Attack on Titan spin-off series, Isayama’s response to Crunchyroll was very direct. He said, “I have no plans right now.” There are already some that exist, however. Attack on Titan: No Regrets is a Levi prequel, Counter Rockets is a Hange prequel story, Before the Fall is a third prequel, Lost Girls tells stories about Annie and Mikasa, and Harsh Mistress of the City follows characters named Rita and Mathias. There are also two comedy series inspired by it, Attack on Titan: Junior High and Spoof on Titan.
As for whether or not another Attack on Titan Levi story could come up, it seems Isayama has an idea for one, but the author noted difficulties that accompany creating a manga might keep it from happening. Here is the quote given to Crunchyroll:
Regarding Levi, I actually have something in my mind, but at the same time, I don’t know if I will be able to write that or not. For example, I have imagined what the story of Levi would be in my mind, but at the same time, whether I am able to output it, that’s a whole other story because writing a manga is a really difficult task for me.
Attack on Titan is streaming on Crunchyroll. Kodansha handles the English localizations and releases of the manga series like the original story, No Regrets, and Junior High.