Usotsuki Omega no Kamasekata

Narumiya, an Alpha and a top performer at a trading company, hates his rival Tsukishima, and is passionate about not losing to him. One night, he saw Tsukushima, whom he thought was an Alpha, in heat?! The secret office love of an elite salaryman (Alpha) and a beautiful and capable Omega who is hiding a secret.

(Source: Shueisha, translated)