Well well well. Another omegaverse but here are 4 second genders, not just 3. there are Alphas, Betas, Omegas and Enigmas. Enigmas are super rare - even more rare than Omegas. And Enigmas tops even Alphas it seems - they may be even able to impregnate them (basically they have the "power" to make Omegas from Alphas maybe even Alphas from Omegas - like... to switch thei gender).
The story:
It starts with a rape in ch. 1 right after some basic introduction of characters is done.
Kanraku Alpha ~Enigma~ 4 verse