Lucia is a 13 year old orphan of European descent, living in North America. At some point in her life she was adopted and later used by the Umbrella Corperation in their experiments. It can be assumed that her adoptive parents were Umbrella employees and were part of the biological weapons program.
For the most part, Lucia was a happy, normal child and enjoyed school. However, at an unknown date she was inducted into the Tyrant parasite experiement and was administered with a tiny parasite where it was would slowly incuabte and grown inside her.
The effect of this parasite insider her meant that over time she began to adapt to the creature and develope certain powers. This included a ringing sensation in her ears when close by a T-Virus infectant, but more impressively, a remarkable healing ability. Any cut or scratch incurred during everyday life would heal almost instantaneously and it was not long before other children at Lucia’s school noticed this anomaly.
This difference made her the focal point of bullies and Lucia quickly became upset in her life, afraid to interact with her peers in case they made fun of her.
During this time, Umbrella was facing its most turbulent time. The Raccoon City Incident had led to the loss of key infrastructure and resources and blame was being pinned on the company. In an attempt to remove future experiments away from mainland America, many operations were shifted to Umbrella Europe.
Lucia was therefore told that she was going to go an live with family in Europe. Whether this was the truth remains unclear, but Lucia (with the parasite still inside her) was given a ticket on the luxurious S. S Starlight cruise liner. Using a civilian vessel was deemed an appropriate method to conceal the importance of Lucia. The ship would be in close proximity to an Umbrella owned submarine and as a failsafe an Amoeba-Type Tyrant was stored secretly on board, ready to be activated in case of an emergency.
In around 1999 Lucia boarded the Starlight unaware of her importance and connection to the parasite inside her. During the trip, the Starlight came under an attack and the Tyrant was released. It infected everyone on board as a failsafe to keep Lucia from being abducted.
Also on board was Leon S. Kennedy and when he failed to report in, his colleague, Barry Burton was sent into the stricken vessel. During his investigation, he found Lucia hiding from the monsters. Barry, being the kind and caring type protected Lucia but in doing so came to the attention of the Tyrant who would then hunt down the pair for the remainder of the mission.
After locating Leon, Barry would then make contact with Umbrella unaware that they were looking to recover their asset, Lucia. Barry’s plan saw him and Lucia board the submarine whereupon the horrors of the parasite were revealed.
Barry forced the resident surgeon to remove the parasite from Lucia’s body but in doing so, the creature escaped, infected everyone on the submarine and then mutated into an Amoeba-Type Tyrant. The removal of the parasite begins to cause Lucia’s powers to decline.
Heading back to the Starlight to rescue a confused Leon, Barry and Lucia find Leon seemingly slumped in the engine room. Barry is convinced, but Lucia who’s powers despite waning clearly senses a T-virus BOW and screams that they were not looking at Leon, but a monster.
This was indeed the case and the fake Leon in front them mutated into true form before being downed by Barry. After locating the real Leon, the three looked to make their final escape before encountering the now fully mutated creature on the East Deck. The parasite grabbed Lucia and jumped overboard, acquiring her DNA in the process. Barry leapt in afterwards and rescued the child.
However, upon making it back to the deck a second Lucia stood alongside them. The creature had mimicked Lucia and was impersonating her. Thinking fast, the real Lucia cut herself with a knife bleeding red blood. It was known that the B.O. W had green blood. With its identity rumbled the three were able to put an end to the mimicking Amoeba creature once and for all.
With the most now defeated the three descended a rope onto the submarine. At this point Lucia realises her powers have now gone as her knife wound had not healed. It is then shown that the Leon beside Lucia has green blood…
However, as Lucia still possessed powers only moments prior with the identification of a fake Leon in the engine room, and she bore full witness to the final confrontation with the parasite, standing next to Leon, the cliff-hanger ending is more likely suggesting that Leon was infected with the t-Virus during an earlier confrontation rather than still being the parasite in disguise…
Lucia is then adopted by Barry and joins Moira and Polly as her step sister.