Original Manga: Chapters, Volumes
Riku Emori, a high school student raised as an alpha, made his debut in elite society at a Shutou family party. The Shutou Family is renowned for being a distinguished household of alphas that wields influence over others of their kind. At the top of this hierarchy stands KeiKi Shutou, the head of the Shutou household, whose charisma commands respect from not only omegas but also proud alphas. From the moment Riku first saw him, he couldn't help but admire Keiki. However, on the night of the Shutou party, Riku's body, which was supposed to be that of an alpha, burned with an unexpected desire and emitted a sweet fragrance...? This is the story of a fated love between two proud alphas α×α(Ω)?!


tl;dr: they temporarily "lost" their magic and is instead borrowing anti-magic from Asta and using that in place of their regular mana.