Up to now, there were three books fitted into one season, but now the problem is that the story is much bigger and it won’t fit in 13 episodes. Now the studio has a difficult decision to make- one option is to cut a lot of content from the source and the second one is to make the fourth installment into a two cour entry.
If they choose the second option, they will need to stretch the story in 24 episodes, so it still isn’t the best choice. However, there is a third option, and that is to wait for the Volume 15 to come out, but then they would have to wait until 2021 to release a two-cour entry that would cover six volumes of the original source.
Even though these options will upset the fans, there is also good news. The upcoming season is expected to have a bigger war than what we’ve seen before.
The author Kurane Maruyama says that the story won’t be similar to anything others have done.