This is an omegaverse story.
A/B/O, which stands for "alpha/beta/omega," is another name for the speculative erotic fiction subgenre known as Omegaverse, which was first known as erotic slash fan fiction. Stories in the genre are predicated on societies where people are organized into dominant "alphas," neutral "betas," and subservient "omegas" in a hierarchy of dominance. These words are drawn from those that characterize animal social hierarchies in ethology. Omegaverse fiction frequently focuses on human behavior that resembles that of wolves or other canids, particularly when it comes to sex. This includes scent marking, breeding, pack structures, rutting and heat cycles, the pheromonal attraction between alphas and omegas, penises with knots, and rutting. It's common to think of male omegas as having a reproductive system. In certain works, a caste structure is introduced, with Alphas represented as the upper-class elites and Omegas at the bottom and subject to prejudice. Though heterosexual Omegaverse pieces have been created, the majority of the works in this subgenre of fan fiction, known as slash fiction, center on male-male pairings.
Marking - The act of biting an omega's nape in order for the alpha to claim the omega as his or her mate. This cannot be undone and is equivalent to marriage.
Fated Mates - An alpha-omega pair who are fated to be with each other.
Knotting - The swelling of an alpha's penis inside an omega during sexual intercourse to make the possibility of pregnancy higher.