The manga of Akame Ga Kill is filled with intense action, complex character developments, and a story of rebellion against a corrupt empire. There are many battles, plot twists, and emotional moments.
The Akame ga Kill manga ran for quite a while. But the exact number of chapters and volumes might vary depending on how you count and which editions you look at.
The fact that the characters in 'Akame ga Kill' have their own dreams and hopes that are ultimately crushed is a big reason it's a sad story. Akame herself has been through so much and seen so many of her comrades die. The sacrifices made by the characters, often in vain, create a very melancholy atmosphere throughout the story.
Another possibility is that the Soul Reapers from Bleach are called to the world of Akame ga Kill to deal with a strange spiritual phenomenon that is related to the Imperial Arms. Some of the Akame ga Kill characters might have latent spiritual powers that the Soul Reapers help them discover. For example, Akame herself could have a connection to a Zanpakuto spirit that she has to learn to control.