[Cosmic Eagle]

Originally Posted by Used Can

Indeed, but consider there are Geass canon works that are manga only, like the Renya manga, Lancelot & Guren, and Oz of the Reflection. Then you have other manga like Re; which is based on events from the TV series (particularly during the Zero Requiem) but expands on them, so there's plenty of manga exclusive material.
Then you have works that are non-canon to the TV Series or the Movie Series, but are still fun to read like Knightmare of Nunnally.
And yet, none of those works, despite being part of the Geass franchise, many of which expand on world events and continue the overall story, have managed to become popular.

I thought Knightmare of Nunnally was pretty popular.....