Citra and Rowan do not want to become scythes, they do not want to take another's life but eventually both of them end up learning from the same scythe and one day on the other side of a war within the system where no one can die and scythes are the only ones who can end a human's life.
Scythe talks about death, grief and what happens if we one day don't need to die anymore, in such a perfect way that I was fundamentally stunned when I started it. The conversations brought up in the story are ones that genuinely need to be discussed and that are explored so well within the story. 
The characters, specifically Citra and Rowan as the main characters, are so interesting and lovable as well as morally grey from time to time that they are ones you want to read about, you want to know more about and that you can't stop thinking about even when putting the book down. 
The downside, for me, to this sorry was primarily that I guessed quite early on what the big twist later in the story was going to be. This led to not being shocked or exited a bit even though I found it quite obvious to figure out. Furthermore, the book took a turn around the last third where some conversations stopped that I would've wished to explored more. 
Nevertheless, am I exited for the next books in the series and can only recommend it!