What, you don't know who Aria is?
She's the "ordinary heroine" the author had cut down and killed off in the very first episode of Akame ga Kill!
This time, she's the protagonist.
Aria: Tatsumi, do you know? Human power actually has its limits in this world. Just like how you want to change this country: even if you topple the Empire, thousands upon thousands of Empires will rise in its place. One day, even the world itself will rot away. And you won't be able to change a thing.
Tatsumi: My lady, what are you trying to say?
Aria: I don't want to be human anymore, Tatsumi! I've decided to become an emissary of "justice" and obtain a joy that transcends humanity!
(PS: This book is fictional. Don't apply it to real life.)
(PS: Aria is a super sadistic young lady. No yuri, no romance, single. If you don't like that, don't read.)