Arceus, recently watching the world and the chaos with in it, it knew humans and Pokemon alike need someone to keep the world from destruction. Dialga, Palkia, Giratina and many other Pokemon throughout the world, one of each Pokemon came at Arceus's call. They all helped grant its wish by agreeing to create a life with their powers and transformations. Using DNA from every Pokemon in the world and the DNA of a man and woman, Arceus used the Pokemon's power to create and quickly grow a human child. This child would bring peace to the world. If an opposite were to be created, than the world would go into chaos by a battle between this child and the dark child.
"Now, go Arcira," Arceus told the child. Her infant is intelligent enough to understand. "Choose a family wisely, grow and learn like any human on this world. When the time comes, you must leave them and pursue what is instructed. If you fail, and turn to the darkness, I and the rest of the Pokemon will tare you apart."
And from the day forth, Arcira was sent to a small village of the earth to be raised by a couple unable to conceive. They took her in, clothed her and fed her. They adopted her and as Arcira grew, she helped her parents and village in the harvest. She befriended many of the Pokemon. All the Ponyta, Rapidash, Miltank, Tauros and Bellossom were best friends with her. Every year after she arrived, the harvest was plentiful. Arcira began her purpose when she arrived. Now that she's reached puberty, the world must now be restored by the power she possesses.