I haven't read the manga of Akame ga Kill, but I have read that it is really different from the anime. They even skipped 10 chapter of the manga completely. Why did they decide to do that? Was it because the show has to be done in a short amount of episodes or something else?
I come with an answer from Polymanga 2015 in Switzerland when the author was there. You can verify it here: Polymanga 2015
The following question was asked and the author answered:
At the beginning of the anime, the manga was already written but in the end the anime exceeded the manga. That's the reason why I want to change the story because the people who had already seen the anime know the end and they will find the manga boring.
It's not his words exactly (I don't remember exactly) but it's the general idea of what he wanted to say.
And after that, he adds:
The end of the anime was fantastic. But the end of the manga will be more fantastic.
For the ones who didn't see the end, let's go see it;)