Although Leona doesn't remember any of this, she was the instrument of the massacre of her entire village, including her loving family. Unfortunately for Leona, she as well as the other members of her childhood village, were descended from the Orochi bloodline. When the Heavenly King Goenitz arrived and demanded their service in his quest to revive the dread god, the elder of the village and Leona's father, Guidel, refused, saying that their village had come to peace with the power in their blood and had no wish to return to the chaotic and violent ways of the Orochi.
So Goenitz, as revenge, used his power to induce the Riot of the Blood in the extremely young Leona, who proceeded to slaughter nearly everyone in the village. Then Goenitz quieted the power raging through her until such time as he might have need of her again, and thankfully for Leona, the trauma of the incident caused her to lose all memory of what had happened. She wandered aimlessly into the nearby jungle, and would likely have died, except she was discovered by an army officer named Heidern. Originally planning to send the girl to an orphanage, Heidern was startled when the child slashed a tree to the ground with superhuman power, and decided to adopt and raise her as his own.
Leona has been raised to be the perfect soldier, an occupation her innate power well-suits her for. She has practiced extensively with multiple martial arts forms and modern weapons. She uses explosives, her own superior speed and strength, the violent energy she can call up, and the support of her fellow soldiers to deadly effect. Her philosophy is to strike hard, fast, and with finality.
Personally, Leona is extremely taciturn. She is entirely dedicated to completing her mission objectives, and while she in fact can feel affection and even love, she rarely lets any of it show on the surface. The only people she is close to are her adopted father Heidern, and fellow soldiers Ralf and Clark. She sometimes has flashbacks to the terrible events of her childhood, but has never quite remembered the truth.