You Should Know I'll Be there For You

Despite what their sweet scent may tell you, Omegas are far from the kind and gentle beings society portrays them to be.

Many who dared to harm an Omega's pup have been reported to have missing limbs, eyes, or fingers/toes from such a foolish mistake. Those are the lucky ones.

tl;dr

Giyuu is not a Beta, but actually an Omega who sees the Kamado siblings as his own pups. Things get interesting, for lack of a better word, when Sanemi stabs Nezuko. Nobody but Rengoku & Ubuyashiki know he's actually an Omega.