Reijou Omega no Hatsujou Made no Nanokakan

Yuri attends a ball in the hopes of being noticed by an Alpha. Raised as an Omega lady solely to marry into a high-ranking noble family, Yuri sits there without any expectations or anxieties, until she meets a man. "You belong to me." This is the sweet and tender seven days leading up to heat for Yuri (Omega), who knows nothing of love, and Jack (Alpha), who wants Yuri all to himself.

(Source: Gentosha, translated)