First Cathedral: Amenti Spire Chronicles. Amenti Spire Chronicles

A century of restraint. Seven years of secrets. One explosive touch that changes the world. Jasmine is a brilliant archaeologist who relies on cold data and sharp sarcasm to keep her distance from her billionaire benefactor, Ben. But when an ancient cathedral collapses around them, they uncover a dormant repository containing World Guide 5: The Final Covenant-a living book that unleashes a torrent of golden wardfire.
When the smoke clears, both of their wrists are permanently seared with a matching supernatural brand. Ben's billionaire archaeologist facade is a lie. He is an ancient vampire, a lethal apex predator who has spent decades using his wealth to fund an underground sanctuary for the supernatural. For seven years, he kept his distance from Jasmine. Now, the magic in their matching marks is eroding their emotional walls, leaking Ben's dark, possessive hunger directly into Jasmine's mind.
With the ruthless Council of Wardens closing in to put Jasmine on a chain, the found family at the sanctuary must prepare for an all-out siege. To survive, Jasmine and Ben must step onto the sacred stone altar, accept the blood oath, and merge their consciousness. They are the Alpha Queen and the World King, and their full union is the only thing that can mend a broken world.