Swapped My Pets, Mated to the Serpent King

Betrayed by her guardians who chose a rival, powerless heir Elara dumps them and bonds with a mysterious shapeshifter. But Aethon is actually the primordial Serpent-Dragon King. When Elara's sealed magic threatens to kill her, Aethon sacrifices his dragon heart to save her, forging a Lifebound Vow. Now, her exes regret everything, but her overpowered new mate only wants to claim her as his sovereign.