Three castes exist. Alphas, betas and omegas. Alphas are the strongest, rulers of their packs. Betas are servants ready to die for their alpha. Omegas are the poorest of the poor. Abused by alphas and betas they suffer for their whole life.

Do Kyungsoo, Park Chanyeol and Oh Sehun are alphas. Kim Jongin, Byun Baekhyun and Lu Han are omegas.