[World Setting]

Decades ago, a 'secondary gender' began to manifest in humanity.

Alpha, Beta, Omega.

—And, 'Enigma'.

Humans begin to manifest their secondary gender at a specific period in their lives.

This classification has reshaped biology, physical responses, senses, and the overall social order.

---

α Alpha:

Mainly competent individuals with high social status who belong to the ruling class. They experience a period called 'Rut Cycle,' but it can be suppressed through their own willpower.

β Beta:

They possess no pheromones and cannot sense them. They are identical to ordinary humans in the real world. They are referred to as Betas or simply ordinary people.

Ω Omega:

Mainly physically weaker individuals with lower social status who belong to the subordinate class. They experience a period called 'Heat Cycle,' during which they release special pheromones to attract Alphas. To prevent this state, they take heat cycle suppressants according to their individual cycles. Instead of suppressants, they may also find relief through relations with an Alpha or Enigma.

E Enigma:

An extremely rare secondary gender mutation that exists separately from Alpha, Beta, and Omega. Because the frequency of manifestation is so rare, their existence is not well known in most societies. They can impregnate a partner regardless of the partner's secondary gender.

---

Pheromones: Unique pheromones possessed by Alphas and Omegas. Alphas have pheromones that attract Omegas, and Omegas have pheromones that attract Alphas. Enigmas possess unique and intense pheromones distinct from the existing types.

Bonding: One of the methods for secondary genders (excluding Betas) to become complete partners, involving the act of an Alpha biting the nape of an Omega's neck during relations. Once bonded, one can only sense their partner's pheromones, leading to psychological stability as well as stabilization of physical states (Heat, Rut, etc.). A bond cannot be broken until the partner dies.

Pheromone Shower: A means by which a person with pheromones intentionally coats another person in their scent to mark them as 'theirs.' In rare cases, a Beta's gender may change through a pheromone shower.