Marking Omega

Tori Yoshida is a 'flawed' omega. Unlike other omegas, he has a unique constitution - he doesn't go into heat, ever since puberty, and can't smell or feel alpha pheromones. While this may be a setback for normal omegas, it's his saving grace that landed him his job as a teacher in a world where omegas are at a disadvantage. Everything is well until he meets the new teacher, Kei Hidaka, a supposedly beta. Things happen, and as it turns out, Kei is actually an alpha, and it seems he triggered Tori's first-ever heat. Now the two have to keep each other's secret from the whole school while maintaining a purely physical relationship. That's all it was, right? (Source: Futekiya) Note: Includes 3 extra chapters.