In the Cardinal World, there exists a country of monsters, the strongest in all existence, ruled by a single, supreme being, known by the name Rimuru Tempest. He is the strongest member of the Octagram—Demon Lord, Chaos Creator—the youngest member of the strongest race, the True Dragons, now the 5th True Dragon and the new God of the Cardinal World, currently sitting on his desk and managing the planet.
It has been a long time since the end of the Great Tenma War. A lot has changed, such as the structure of the Octagram, since a few members decided to ditch the concept of the Demon Lord entirely and change it to the Overseers of the World. Why, you may ask? Well, because the title 'Demon Lord' sounded too violent and, frankly, scary.
But that's a story for another time. Let's get back to the truly juicy stuff.
Right after the end of the Tenma War, Veldanava decided to ditch his responsibility as God and spend his time with his wife, Lucia, inside Rimuru. (Apparently, this is possible by giving Ciel most of the knowledge of the Overworld to enable travel between different creators' worlds.)
Following her father's example, Milim gave up on managing anything (like she ever truly did). Seeing the behaviour of her creator and the need for a replacement, the Voice of the World decided to find one. Now, guess who the replacement is? Is it Rimuru? Oh yes, it is. He was given the job of managing the entire world, like he was not already doing exactly that.
After 5 years, Guy decided to follow Milim by retiring as the Moderator and crashing in Tempest along with Velzard. Apparently, it was booing in the northern continent.
Then, after a few years, the soul of Masayuki was repeatedly destroyed due to his ultimate skill. It was later found that if a being's will is weak, the ultimate skill can abandon the person, which resulted in Masayuki's death. So, Rimuru decided to simply rebuild him without his ultimate skill. Now he dies and comes back to life like a phoenix.
Velgrynd was truly sad that her love could no longer exist as a human, so she decided to follow her older sister's path and came to Tempest along with him. Since she knew Rimuru could just recreate Masayuki again if he decided to drop dead, she joined the group. After a few years of playing, she became a glorified otaku along with Milim, Luminous (who also got bored), and Veldora.
[Author: Yup, the Tensura is truly a world full of otakus.]
Rimuru: "Hey, Ciel. I am bored. Is there anything interesting going on in the world?"
Rimuru asked his true partner, the truly omniscient Manas Ciel, and his only wife. (Yes, the Waifu War is still going on as free entertainment.)
Ciel: "No, Master."
Ciel responded to Rimuru in a sad tone, but suddenly sensed something interesting in the Overvoid. She then told her master that she had found a world where a war was going on, and that world's God had left and ascended into the God Dimension. Therefore, traveling to said world is possible.
Ciel: "Do you want to go there, Master?"
[Author note: OK, we know there is no God Dimension, but we have created it to house "All so-called dead GODS" like in Naruto/Boruto, High School DxD, DBZ (Zeno is no god), etc. So these now hold a God-like being and can look after it.]
Rimuru, upon hearing Ciel's words, was overjoyed.
Rimuru: "Yup! Ciel, I knew that you would find something for me in the entire Void."
Ciel, upon hearing the words of her master Rimuru, started to blush and became as red as her eyes. Sensing this, Rimuru goes to an imaginary space and continues teasing Ciel.
Ciel: "Master, stop it." (Ciel makes a super cute face.)
Ciel: "Master, the power level of the world is too low for your true existence, so we need to create a pseudo-body for the new world."
Rimuru: "Well, what about the Cardinal World? Who would look after it?"
Ciel: "Master, don't worry about it. Since it is our vacation, I will dump all the work on the useless otakus in Tempest."
Rimuru (crying joyfully): "Yes! I am free! Suck it up, Guy Crimson."
Ciel laughed along with her master on how to prank Guy and the other otakus. They finally arrived at a plan to dump paperwork on Velgrynd and Velzard. The Moderator's work falls to Guy, along with Luminous and Veldora, who will do all the work in the Labyrinth. Dino and Feldway are among the observers of Heaven, along with Frey. And Kagali, Carrion, and other Tempest executives will look after every major state of Tempest. Milim is to do the paperwork of Heaven, and her secretary is Shuna.
Well, what a devious job has been created, as if it should have been in the first place. They send their job via the Voice of the World, so they can't ignore Rimuru's order.
Finally, Ciel activates her master skill [Ultimate Skill: Void God Azathoth], sending her master to the end of space and time, and also slowing down the flow of time in the Tensura verse, ignoring the cries for help from all the Demon Lords and Overseers.