The Alpha That Rolled In

After joining a gang organization, Sanghyeon belatedly manifests as an omega. Deciding that, since he has manifested as an imperfect omega anyway, he will live his life hiding it forever, he tries to keep it under control.

He ends up witnessing Do-yoon, whom he has raised like a son for the past ten years, going through his rut. Sanghyeon had always thought it was just a late-blooming puberty, but Do-yoon is actually an alpha. And not just any alpha, but an alpha of superior genetics. Worried that Do-yoon might suffer permanent damage, Sanghyeon anxiously ends up helping him through it.

(Source: Kidari Studio, translated)