Legend has it that seventy million years ago, human survivors of a catastrophic disaster from other worlds arrived in this world and received the protection of the landowner, surviving on this land and starting to repopulate again. Humans served the landowner as kings, and the landowner recognized them as subjects, and both sides established a covenant.
The landowner was immortal, devoid of emotions and desires, ignorant of love, and basically spent their long lifespans in slumber. Humans, however, possessed abundant emotions. The landowner became curious and thus added a drop of human blood to their crystal-clear hearts. The crystal hearts began to change color, first black, then blue, then yellow, and finally turned crimson.
In an instant, the landowner understood emotions and desires, and fell in love with the owner of that drop of blood—a human girl.