A promise, a vow

Sigma.

A name both familiar and foreign to Lucian.

He remembered once reading ancient records about this elusive classification.

Sigmas had once existed alongside Alphas, Betas, and Omegas. These individuals bore the aura and pheromones of an Alpha, yet possessed the reproductive ability of an Omega. Uniquely, they could conceive with an Alpha, a Beta, or an Omega.

Conversely, because their seed was rare to the point of near nonexistence, Sigmas couldn't impregnate others, unless the partner was also a Sigma.

Sigmas were unaffected by pheromones, immune to an Alpha's dominance, unmoved by an Omega's allure, and held no desire to rule. A lone wolf, detached from the pack, with a will and purpose all their own.