The anime is set in Tokyo, the country is haunted by Ghouls( They devour humans). One day a normal college student ends up being attacked by a Ghoul called Rize, he survives the attack but is injured badly, he needs organ transplants because of the injuries, since they cant contact his family the doctor transplants the ghouls organs in to him, on the end hes both Human and Ghoul
I think the main point of the anime is that he lives life both as a human and as a ghoul and sees both sides