Sentence:  When Yuri goes into his first <WSD>heat</WSD>, it is not only an uncomfortable and traumatic physical experience, it is also an identity crisis: this is the moment realizes that he is an omega, and not a beta as he had previously assumed. 
Meaning of the word marked with <WSD> tags:  In omegaverse fan fiction, a cyclical period in which alphas and omegas experience an intense, sometimes irresistible biological urge to mate.