Princess Serenity lived on the moon in the past along with her mother and her protectors. It’s known that as Usagi, she also wasn’t a person who loved study, she preferred having fun, and even more she loved spending time with Endymion, the prince of the Earth, even if it was forbidden.
During the series we get some glimpses of her life on the moon, and what kind of person she was. Even if her life ends in tragedy, it’s shown that Serenity had a great life, surrounded by the people who loved her and she loved in return.
She was born as a crown princess of the moon, whose job was to protect the Earth from the far, but she fall in love with an earthling, the crown prince of the planet and from that moment she lived for him. When Metalia gathered the army and attacked moon, she tried to kill her, but in the end killed Endymion who protected her with his life, seeing her beloved had died, Serenity killed herself, because she wouldn’t have been able to live without him. Her mother managed to pull the strings of fate and made her possible to be born on earth as Usagi Tsukino.
Her princess dress is quite similar to the one that dresses Neo Queen Serenity,
she is without a crown (even if in some arts we can see her with one) and the
ribbon at her back is smaller than the neo queen’s.