The headstrong daughter of Silver Millennium’s Queen who bares the same name, Princess Serenity often explored the earth to admire its greenery even though it was forbidden. There, she met and fell in love with the Crown Prince of the Earth, Prince Endymion.
In the manga, when Queen Materia attacked the Moon Kingdom, Prince Endymion died protecting Princess Serenity, and she committed suicide in her grief. In the anime, however, they were both killed, and later resurrected on the Earth in the coming 20th Century.
I actually find the use of yellow eye shadow most interesting in this cosplay. Quite a rival for Usagi’s cosplay, don’t you think?