My Fiancée Is a Mermaid

When Gojo returned from a mission, he discovered that he had somehow acquired a fiancee, and heard that she had a special identity. The handsome silver-haired boy scoffed. "I don't care whose daughter she is. I'm too busy, and not interested in dating." Later, he saw the so-called "fiancee" sleeping in a huge aquarium, her pale blue tail shimmering with an unusual sheen. When she woke, she approached him with a mixture of fear and curiosity, and addressed him in a soft, pleasant voice: "Mr. Gojo." Geto smiled beside him. "Satoru, if she's a bother, I can take care of her for you." Gojo: "...What?" Note: 1. Everyone survives in this alternate timeline. 2. The plot exists to serve the romance, with a conventional redemption arc. 3. The pairing is Gojo from his Jujutsu High days, who later grows into 28-year-old Gojo. Theme: Happiness is life's first priority.