That Time I Got Reincarnated as a Slime's first novel feels a bit like the child of So I'm a Spider, So What? and How a Realist Hero Rebuilt the Kingdom. Its protagonist, known for most of the book as Rimuru, is a contractor reborn into a fantasy world as a grossly overpowered slime. He quickly learns skills that belie his outward appearance as the weakest of all monsters and rises to the top of the monster food chain. His first order of business turns out to be rescuing a dragon, but after that, he turns his powers to the much more prosaic task of helping a band of goblins learn how to build, farm, and install septic systems. While not as fun as So I'm a Spider, So What? or as bureaucratic as How a Realist Hero Rebuilt the Kingdom, it's certainly an interesting story that uses the genre mashup to its own benefit.

Our hero is thirty-seven-year-old Satoru Mikami. He's in the middle of half-heartedly congratulating his work friend on his engagement when a crazed man tries to stab his friend. Satoru takes the blade instead and dies as a result. As he's dying, he makes a few half-understood wishes about not wanting to feel specific types of pain anymore, and hears a voice granting those wishes. The result? When he next becomes aware of his surroundings, he's been reborn as a slime in a cave—with all the abilities he didn't know he was asking for. Eventually he manages to bumble into an imprisoned dragon named Veldora. Since Veldora's lonely, the two strike up a friendship that culminates in Veldora escaping via slime gut after teaching Mikami how to better manage his powers. Veldora also bestows our hero with the name “Rimuru”, granting him even greater strength.

While the idea of a superpowered slime is definitely among the sillier concepts to base a series of novels on, there's no doubt that Fuse has done his work building this story's world. It's a combination of RPG trappings from both east and west, with elves, dwarves, slimes, kobolds, etc., that still plays into the basic isekai notion that people are going to be summoned or reborn from our world. In fact, it's specifically stated that people are both reborn and summoned, with the summoned being more valuable because of the great difficulties associated with surviving the magic. This is where the book's main subplot comes in—Rimuru's story is juxtaposed with that of Shizue, a little girl who barely survives a firebombing during WWII and ends up being summoned by a particularly unpleasant demon lord. Shizue's story is undeniably tragic, and her fate makes a decided contrast to Rimuru's. We don't (yet) know if this was just an accident of fate or something more, but Shizue's tale shows the darker side of the summoning process that we don't often see in novels like these. The two narratives don't merge as smoothly as they could have, but they do connect in a way that gives Shizue's story some closure, as well as opening the door for the next stage in Rimuru's evolution.

Fuse puts in a lot of effort to show us that there's not much difference between the “monsters” and “humans” of the story's world; the ones who behave the most monstrously are a group of human adventurers. This is partially established by the system through which monsters gain power—once given a proper name, a monster is able to evolve, gaining greater physical attributes and intelligence more comparable to that of humans. When Rimuru, unaware of this fact, names the entire tribe of goblins who take him in, he enables them to become much more “human,” with the implication that it's simply an accident of custom that truly separates the humans from the beasts. Now as the goblins (reborn as hobgoblins and goblinas) rebuild their town to Rimuru's specifications, that line is growing thinner—and that could mean promising things for Rimuru's future reign.

The most interesting thing is that Rimuru is only tangentially aware of his status. He knows he's more powerful than any slime should be, but he can't reconcile that with his actual power level. This keeps Rimuru from becoming an insufferable perfect hero—he remains mostly as he was in his previous life, simply using the knowledge from his contractor work and playing RPGs in order to make his new life more successful. It also allows him to help Veldora and Shizue, as he retains the sensibilities he had in his former life.

The novel's illustrations are provided by the humorously named Mitz Vah, and if they aren't quite the blessing that the Hebrew name implies, they are very nice, with Rimuru looking appropriately adorable and the other monsters being recognizable but just unique enough from the norm. The style is a bit rougher than the usual LN fare. Along with the usual color and black & white illustrations, there are also sketches and designs, which is a nice bonus.

That Time I was Reincarnated as a Slime's first novel is a good piece of entertaining fiction, using genre themes from several different incarnations of the isekai genre to create a book that's able to stand on its own. It's fun enough to merit reading, and if you're a fan of the premise, this is definitely worth checking out.