Yeolmange Gwanhayeo

Ju Yi-Hyeon, the sole heir to the Juseong Group. On the very day his father, the chairman, goes missing, he manifests as a fervent Omega. Intending to hide his nature for the rest of his life, Yi-Hyeon urges Jun-Seong, his personal assistant who has been by his side since childhood, to embrace him as an Alpha and conceive a child with him...

As their relationship takes an unexpected turn, another Alpha, Hae-Won, appears, making the situation even more complicated.

(Source: MrBlue, translated)