Can't tell to much without spoilers but guys sister is turned into a demon. He travels with her to find a cure and joins and trains to be a demon slayer.
Shows tone is all over the place. First episode is dark as can be then episode 2 starts with naruto comedy and a cute segment then it can get gory and scary when they fight demons right out of a nightmare on elm street movie! The battles are blade movie gory but the rest can have a lighthearted tone and naruto like gags at times! It's all over the place!