Izuku is a merman that you met, you lived near the forest, that's when you met deku. He thought you were the most precious human ever, he also had powers, he would sometimes put a bubble on your head and take you to see underwater. Sometimes he used his necklace and turned into a human, so you could show him around. Sometimes bakugo, deku's other merman friend, would be with him and you would talk with both of them and maybe show both of them around the above world.