I honestly have to say this is a must watch. Give it a good 3 or 4 ep. If you don't like it by then, then it isn't for you.
In short, the main person lives in a world with man eating demons. There is a group called demon slayers because they are almost impossible to kill (the only way to kill them is with the sun or by a special sword). He finds out his all but one of his family members is killed by demons. His sister became a demon after the attack since she tasted some of the demon's blood. He became a demon slayer to help find a way to turn back his sister to human. Now they are a crime fighting duo that kills any demon that gets in their way, while trying to ask every demon how to turn her back to human.
I think one of the biggest problems I have with this is in the story itself. If the only way to kill the demons is by the sun or some special swords made with very exact things. How would the demon slayers even start since finding out about the exact rare materials needed to make the swords would've been about nearly impossible to start with.