Ikaru is the surviving princess of Atlantis( in the original anime "Triton of the sea", she is a little mermaid named Pipi, but I don't like her name and character), at last, she had become Triton's girlfriend.
You see that she has no hind limb(legless) and looks like a half-serpent( Naga) in the picture, because she's too young —still in the infancy form of (anthro) eastern dragon. In fact, she belongs to the same species as Triton Draco.