Akame ga Kill! Zero is a prequel manga series based on the titular character Akame before she joined Night Raid.
One-on-one fights are the best to watch, especially the action sequences that depict the movement and grace of the opponents. But in a standoff, only survival matters, as the ball of tumbleweed rolls across the opponents signaling the fight. And if it's a dark fantasy anime, then Akame ga Kill! takes the top spot.