Frank is not a traditional omega by any definition.
He can't cook. He has no nesting instinct. He doesn't submit easily, and he likes fighting a lot too much.
He likes getting fucked though.
Maria is petite and fragile-looking and gentle, the opposite of the alpha archetype but she gets Frank going the way nobody else quite does.
He ends up on his knees in front of hear, sucking at the head of her dick until it slips from its sheath above her vagina and damn, that thing's big, especially for such a small alpha.
He wraps his lips around it, hardly able to fit more than half into his mouth and sucks, nursing at the head until it jerks and oozes more slick over his tongue, and she clenches down on his fingers.
She pushes him away then, not wanting to come in his mouth.
Tells him to get on all fours and slips her fingers inside to check how wet he is (very, he's dripping despite not being in heat). Then she rams in in one long, steady, glorious stroke.
He likes being knotted. By Maria at least. Likes how full, stretched he feels with her knot, how every motion sends little waves of leftover pleasure through his body. Likes the heavy, sloshing sensation of her cum inside him, the way she lies half on top od him and rubs his belly and asks if he's going to give her many healthy pups like a good omega.
There is no possibility of course, they used a condom and neither is in heat, but the very idea is almost painfully arousing.