The daughter of a policeman and a dance instructor, Rebecca is thought to be popular because she has big eyes, a small face and slender limbs – similar to the cartoon characters.
There is much more at the link, including videos. The upshot is this:
Rebecca, from the Isle of Man, first came to attention on YouTube where millions watched her dance to J-Pop (Japanese pop music) and the theme tunes of anime cartoons.
She appears in hundreds of clips dressed as Japanese cartoon characters.
Her new album is expected to go straight to number one in Japan. For the pointer I thank LongTermGuy.