A long time ago, when Darien was a little boy, his entire family was in a car crash. Both his parents died, and he had amnesia afterwards. He never knew that he had had a little sister by the name of Cynthia. During the crash, Cynthia's car seat somehow managed to get outside and into a creek. She was found a while later and adopted. Not knowing who her parents were or what they looked like, and only remembering two adults calling her Cynthia and waving a stuffed clown in her face, she made it her ultimate mission to one day find her family.
At the dawn of time, an entity was born in the Sun, to be awoken to fight evil when it reached its peak. It awakened from its home during the attack on the Moon Kingon by Queen Beryl and her shadow warriors. However, Queen Beryl saw this upcoming opponent and quickly used her most powerful spell to confine the entity in the Sun for all eternity. Still awake, the entitity continued since that day to fight the spell and break free of its prison.
When Sailor Moon healed Aurora, it sent a shockwave of energy throughout the universe, which destroyed Queen Beryl's spell and released the entity in the Sun. The entity sought to choose a valiant mortal of Earth to behold its powers, and it chose Cynthia. Throughout her life, Cynthia had been shifted from one foster family to the next. And shortly after the healing of Aurora, the entity combined its life force with Cynthia, giving her a flash of knowledge: that her family was in Tokyo.
She ran away from the orphanage to Tokyo. Once arriving, with just a little money left, she entered the Crown Parlor to get a sandwich, where she met and quickly became friends with Serena. At the Cherry Hill temple, while eavesdropping on the Sailor Scouts, she got into a conversation with Grampa, who, since Cynthia hasd nowhere to live, decided to take her in as a house-guest like Chad. The first time a monster from the Negaverse appeared, Luna noticed the planetary symbol of the sun on Cynthia's forehead. As the scouts engaged the monster in combat, Luna conducted a mind-meld with Cynthia, unlocking the powers of the entity of the Sun and forging the Sun Locket, which allowed her to transform into Sailor Sun.