My Worthless Ex-Husband Is Poseidon, God of the Sea

Kael is dying, and he uses the Oath Emblem to summon Thalen, the Sea God. The Emblem can grant any wish, and the wish Kael makes is a soul bond lasting three years between Thalen and his granddaughter Serena, so that their clan and the sea citadel will survive. Kael got the Emblem a hundred years earlier, when Thalen cleared the Maris Sea of monsters and stopped a tsunami that had been prophesied, and Kael was among the people he saved. Thalen takes the bond. He hides that he is a god, marries into the family passing himself off as a blacksmith, and keeps the Sea Barrier standing without telling anyone he is the one holding it up. Serena treats him as a disgrace to the house. Then Lord Cedric comes back. Cedric claims Thalen's work as his own, pins a charge of treason on him, and Serena believes him completely. She demands the bond be broken. Thalen agrees without a word of protest and takes his power back out of the barrier. The runes on the barrier begin to fade, and the tsunami reaches the citadel.