Overlord is a Japanese dark fantasy or Isekai anime series based on a light novel series. The novel series is written by Kugane Maruyama and is illustrated by So-Bin. There has been a manga adaptation of the same, which was published by Kadokawa Shoten on November 26, 2014. After then the anime series directed by Minoru Ashina premiered on July 7, 2015.
The producers had announced that the anime would return with the fourth season. They aimed to release it by July 2020. But due to the conditions given right now, the production slowed down. Mostly it has been discontinued. Therefore, the series has been delayed to release after 2020 for sure. But as nothing can be predicted in the conditions prevailing now, no exact release date can be announced.
The fourteenth volume of the manga took a big-time hole for publishing. Accordingly, the fourth season too, kept on getting delayed.
The fourth season will showcase the power and strength Aniz is capable of. He is going to prove himself by showcasing his worth. He will fight against the obstacles and stand ahead of them by governing Sorcerer Kingdom.
Though Aniz has been ungratefully trapped inside the video game, he will make sure that as the warrior king there, he will perform his duties and form a strong empire. After defeating Gazef Stronoff by killing him, Aniz realizes that he is way more powerful than he estimated about himself.
Some fans have even theorized that Aniz may be showcased as a negative character or as an antagonist if the creators take him ahead for ruling the kingdom. Well, what and how the story proceeds is a matter to be revealed when it is ready to release.