You Sacrificed Poseidon's Daughter, No ForgivenessEpisode 4

She gave up her divine identity and sealed away her powers, all to marry a mortal prince—only to discover that the prince loved his adopted sister. During those years, she endured three years of his coldness and torment. On the day she was offered as a sacrifice in the prince's sister's place, she fell into the abyss—and rose again as the daughter of Poseidon. When he learned the truth, his regret ran deep.