The 4th volume of That Time I Got Reincarnated as a Slime covers episodes 20-23 of the anime. Episode 24 dealt with a side story not featured as part of Volume 4’s main plot. This is the point where we start to see some disconnect from the books. The anime skipped over a fair amount of material from Volume 4. Some of these events were watered down in the anime and get summarized quickly. Others are skipped over entirely, removing sub-plots from the story. Overall, about half of Volume 4 was cut from the TV show.
The first part of this book deals with the aftermath following the big battle at the end of Volume 3. As the Jura Tempest Federation continues to grow, Rimuru’s life becomes more political. At the beginning of all this, he was just some guy. Now he is the ruler of a country with thousands looking to him for leadership. A little self-reflection on this fact makes Rimuru realize the full implications of his new position and he starts to make additional arrangements to ensure the Federation will be a lasting thing. At the same time, his own desires and a promise to an old friend also start to influence his choices.
Compared to the first three books, the stakes are not high here. There are stakes, but not on the level of Rimuru and co. being wiped out if they fail. In this book, their lives are more everyday (or as close as possible for them) instead of being thrust into another massive battle. The story here also expands on Shizu’s backstory and what Rimuru’s promise to her ultimately means. Getting extra development for a character whose personal story is already wrapped up is rare, but the way FUSE does it works well.
One annoying thing about Volume 4 is the cliffhanger. The book ends on a high note, but it’s still singing once you reach the last page. But overall, this was a solid volume in the series. Not having any major events happen let FUSE spend more time world-building instead. The cliffhanger does show that Rimuru will be back in the action during the next book. This cliffhanger is another piece of content cut from the anime (though they do foreshadow it). Presumably season 2 will start with it. With a new season of the show confirmed, here’s to hoping the anime continues to adapt these books well.