All I’ve read about is lamprey stew in Spain. The lamprey’s blood is put into the simmering broth in the last few minutes to form a dark rich soup. This is then served in a clay pot with a lump of rice in the middle.
I’m Asian and I know at least three Asian countries that put blood into the simmering broth. One of course is my country, the Philippines. For some reason, Filipinos like to eat this soup with steamed rice cakes (not rice.) But I was surprised when I read the Vietnam war exploits of the five fingers. The Vietnamese, during a feast, initially served each soldier a pot of the same soup and a large chunk of corn bread which they dipped into the blood. And then there’s a chicken soup in Malaysia that’s also enriched with chicken blood (they’re Muslims, it occurred to me.)
Wiki lists some types of blood soup, like the already-mentioned czarnina and svartssopa, but also mentions blood soups from Lithuania, Finland, Czech, and Mexico.