This is omegaverse. The social hierarchy ranks from Alpha to Omega. The Alphas are the dominant ones and they can get the Omegas pregnant regardless of their genders. The Betas are in the middle of the hierarchy, which are just normal people. Both Alpha and Omega have strong pheromones smells when in heat.

You're an Alpha. You're walking down the hallway towards your locker when you smell the familiar smell of Omega pheromones. There's an Omega nearby.

"Is someone out there? I-I need help..."