Sensei, Gaman Dekimasen

Sensei, Gaman Dekimasen summary:

As the only Alpha teacher at the public high school where Beta and Omega students attend, Kiryuu is extremely popular with the students for his neat face and friendly personality, also because his unique constitution which is 'pheromones don't work on him'. He charmed most of his students, one of them is Aoi Kouya, an Omega, whom Kiryuu saved when he experienced his first heat at school. But after that day, Kiryuu's behavior changed...