Pheromone Baby

Beta Ji-Han, who had a close relationship with his childhood neighbor and younger sibling, Yun-Seo, ended up in a relationship with her by accident. Afterwards, Ji-Han learned of the sudden pregnancy and that he had manifested as an Omega. The father of the child was undoubtedly Yun-Seo, an extreme alpha, but Ji-Han decided to terminate the pregnancy for the sake of Yun-Seo's future as a college student. However, Yun-Seo readily confessed that both Ji-Han's pregnancy and his trait change were part of his own scheme... “You were always my omega, you've always been mine.”(Source: MrBlue, translated) Note: Includes three extra chapters.