That aside, I'll put aside the seller-style description of this story to get to the juicy parts. Just know that there will be very slight spoilers about the start of the story, but honestly, you can probably tell who's who and what'll happen at the start just by looking at the cover image.
This story is mainly about the Demon lord, Maou, and the Hero, Yuusha (In this case, Yusa). Forced to set aside their differences for the time being, they work in Tokyo to try and make a living, while they make a few friends, most who end up being from their own world anyways.
But it's not just about two strongly opposing forces becoming "friends" and making friends. Behind the thin veil that is a friendship is lots and lots of (mostly) internal conflict, which comes from both of the pasts of these two special individuals.
You'll have to read the story yourself because if I were to say any more I'd be spoiling a whole bunch, and I don't want to do that.
The story (Which, apologies, but I refuse to explain further due to big spoilers) aside, let's talk about the other aspects.
Fan service is low. Now, personally, I'm no fan. I love fan service. However, I don't love pointless fan service, and Hataraku Maou-Sama! is perfect in this aspect. The only unnecessary fan service in this story is Chiho's massive jugs, and even then, the writer (Satoshi Wagahara) manages to actually add plot advancements with those very jugs.
Yes, there is romance in this story. However, the romance isn't the primary focus of the story, and I can respect that greatly. Maou-Sama offers a good story that uses every single aspect of it to advance its plot, and it does it very effectively. It answers all your questions, only leaving behind ones that are meant to be left behind. The plot of the story isn't too elaborate, and it doesn't involve any logic that's out of this world, save for their own language. Even their belief system is loosely translated from ones that are of this world, simply taking metaphor and turning it into a reality inside the story. (Of course, by "belief system", I mean "the people believe in it as myth, but it's actually real")
The art is extraordinary. Seriously. Fine detailed fights and fine detailed tiddies, I have not a single nanogram of complaint. It's got a simple yet complicated feeling to it which in the end makes it feel glossy, refined, yet still innocent.
Character development is very good. Even our comedy relief characters (Chiho, Ashiya, etc.) have backstory and have serious personalities when they need to. The characters don't take shit pointlessly and don't feign ignorance when something seems off. Nobody is an absolute airhead, basically, and I absolutely love it.
And last but not least, the enjoyment. It's great. I had a fun time watching the anime and had an even better time reading the manga. The fluidity of the plot, the interactions between the characters, the pleasant art, and the comedy is great. What I love the most, though, is that the story manages to have romance and comedy in it, but not convert into a typical romcom, even though the story could totally allow that to happen. While the comedy is playful and highly sarcastic, the romance is deep, rough, and not at all a thing that could be joked about to any of the characters, lest they felt the need to be cynical and suicidally sarcastic about it.
Overall, Hataraku Maou-Sama!, or The Devil is a Part Timer! is a hands-down must-read if you enjoy a good story with a steady plot, as well as a good bit of comedy to go along with it all.
