Gojo Satoru is a mermaid of light, Suguru Geto is a mermaid of darkness

Gojo Satoru was supposed to become the strongest, but still... hasn't found a mate. Usually everyone found a partner for the future when they were 12 years old, but Satoru was already 16, and he still couldn't feel the pheromones of his mate!! He always thought that something was wrong with him, but... one day, when he was sailing the sea, he decided to go to the depths. Having swum there, he came across a rather interesting cave. At first it was very dark there, almost nothing could be seen, so he had to feel his way through.. but suddenly a bright light flooded his eyes. And then he saw.. him. It was a boy, about 15 years old, if not younger. His hair was thick and black, and also long. His fishtail was like the night sky, and shone like the stars, and the boy's skin was pale as marble. Combing his hair with his eyes closed, the boy hummed a melody. And also.. Satoru could sense the boy's pheromones. Wait, he could sense pheromones?! Could it be.. this is his mate..?