One person's Utopia is another's Dystopia.
In Neal Schusterman's Scythe, death is a thing of the past. If you fall off a building and "splat," you can be brought back. When you get old, you can reset to a younger age. Thanks to nanites, no one gets sick. And the Thunderhead (think nice/nonevil AI overlord?, idk) keeps everything running smoothly. But with the population still growing the options are either no one gets born or some people must die. So the Scythes were created. Scythes are humans who have the authority to decide who dies. They have rules and a strict set of guidelines about how many people they kill or "glean." They can't focus on any one group, or age, or gender. They can glean by whatever method they prefer, and the family of a person they glean gets a years worth of immunity from being gleaned themselves. Scythes can't glean another Scythe and the family of a Scythe gains immunity from being gleaned for as long as that Scythe is alive. It's a system that works. Scythes are feared and adored, viewed as necessary to protect everyone.
But it's not a job that everyone wants or should have. And when a Scythe picks an apprentice, that person's life changes forever. When Citra and Rowan are both picked by Scythe Faraday as his apprentices, neither wants to be there. But nobody says no to a Scythe (it's kinda like the mafia). They have one year to learn the skills of a Scythe, pass three tests, and become Scythes themselves. There's only one open slot so whoever fails will go back to their normal life.
But no Scythe has ever taken on two apprentice at once, and, as punishment, a choice is made. The failed apprentice will be gleaned. With political machinations backing them into corners, Citra and Rowan have to decide if they really want to win and what they're willing to be turned into to learn how to kill. And do they even want to win when they're falling for each other? (Romance. Duh duh duh.)
Scythe makes you think about what you would do if you could kill to save humanity, and how you would do it, and why. So if you're looking for that fun uplifting book... then maybe not this one. (Puppies and kittens this is not.) At the same time ... it's not super dark? It's a thought piece that will take you on a twisted ride about how the world would work if nobody dies naturally, and what it would be like to have to kill. You get the light(ish) side and the dark side of that. The romance element is present throughout the book, but it really isn't the main focus. There's some action too, but the book is really about the emotional toll becoming Scythes takes on Citra and Rowan. It's a cool sci-fi that's as horrifying as it is enthralling.