Good boy (Omegaverse Sebaciel)

Has adult content I'm not going to tell y'all if you want to read it you can read it, but please be 18 or older. And please be careful. This is a fanfic of my idea like a what if?
Alphas- Are rare but not as rare as an omega, can mark omegas, are dominate, and claiming them as theirs. Can let out pheromones that make omegas obey them and submit.
Beta- Can't smell pheromones, more populated aka not rare.
Omega- Have heats, tend to be stereotypically weak. Can let out pheromones when they are scared or when they feel threatened usually have blockers to make sure that they don't have any scent that Alphas can smell. Omega are the only ones that can get the ears and tail to come out in their human form. They do it whenever they want or whenever they get too scared that they pop out. When they came out it is called omega/human form.
Ciel is 16 years old and is a omega.
Sebastian is a demon and one of the strongest Alphas on earth and hell.
This Ciel is the fake Ciel that we know so I'm going to make him have a twin sister instead of a twin brother. And I did look up the name for the twin sister that is named Alice Phantomhive. In the story he doesn't have a twin brother. So Alice is 16 years old and is a beta.