Ew existence's Manga

On an island isolated from the rest of the world, technology has no place. At the center of this population is the monastery and the cult of the Inagi, children with white hair with supernatural powers who are indoctrinated by the monastery. Their role is to fight the monsters of the black sea. Our heroes meet and spend 10 years together. The seed has a special power that is to heal the inagi of these black spots that grow on their bodies and end up killing them. The monsters of the sea only dream of becoming human and sometimes manage to possess some of them. The father of the seed was a hybrid and to give birth to the very first finally born of the sea and humans, allowing him to have these healing powers. With people from the outside world, he tries to find the answers to these mysteries