Obviously Lu was looking for his little bro-
(Okokok-here's what I got-AHEM-
Prince Midoriya is a merman, the youngest of his 6 brothers and sisters (Koda, Jiro, Mina, Ojiro, Momo, and Shoji). Fascinated with the surface world and the humans who live there, Deku is constantly getting himself into trouble with the assistance of his best friend Uraraka. His fathers and the kings of the ocean Aizawa and All Might have strictly forbidden anyone from going above the water due to the land people's dangerous nature and as such are dismayed by their son's fascination, sending their advisor Iida to watch over him.
Meanwhile in the castle by the sea, Todoroki struggles to contend with the pressures of being heir to the throne and the cruel nature of his father, not wishing to be the sort of king he is. While his father is attempting to force him to find a suitable queen, Todoroki is perfectly content to sail the seven seas with his right-hand men, Bakugou and Kirishima.
When a chance encounter between the two results in Deku falling for the human, the bitter old sea witch Chisaki(Overhaul) sees an opportunity to claim the ocean for his own, sending out his servants Toga and Twice to spy on the little merman. However, a mysterious entity pulls the strings from behind, working to destroy the merpeople's way of life as they know it.)