Sylvia Carla Santiago was the daughter of Dominic Santiago and Maria Flores, sister to Benedicto Santiago. The youngest of the two Santiago siblings, Sylvia was born just before the landing at Aspho Point and Dom's eighteenth birthday.
Sylvia Santiago was born on the day before the Battle of Aspho Fields. During which, Sylvia's father, Dominic Santiago, and uncle, Carlos Santiago, were present. Maria had given birth to Sylvia prematurely, and gave her middle name, Carla, in honor of her Uncle Carlos. Carlos received the message first, then sent the message to his brother. Unfortunately during the battle, Carlos was killed.
During the next two years, Sylvia grew up with her older brother, Benedicto, and their parents in their apartment in Jacinto. Sometime after, Dom and Maria purchased a house in Ephyra for the kids to grow up in. Sylvia had her own room and was filled with stuffed animals. She was particuluary fond of her stuffed, green-striped caterpillar and took it everywhere.
The Pendulum Wars had ended two years after Sylvia was born, and her father was on permanent leave. Maria, wanting to give herself and Dom the day off, sent Sylvia and Bendedicto off to their grandparent's new apartment. This day was Emergence Day, when the Locust emerged and overran Sera. Sylvia, Benedicto, and Maria's parents were killed by the Locust. Maria and Dom were unable to bury Sylvia and Benedicto, but were able to bury Maria's parents in the family graveyard in her hometown in Mercy.
Maria continued to blame herself for their deaths for years, and eventually began to hallucinate that they were still alive, searching for them when she could.
Dom keeps track of how old his kids would be if they were alive in which he indicates that Sylvia would be seventeen during the time of the Evacuation of North Gate. However, even though Dom has been in grief for a long time, Maria was suffering from Post-Traumatic Stress Disorder. Her depression lead her to go weeks without speaking or eating. Eventfully her children's death lead her to leave Jacinto and to live with the Stranded.
- The Slab (Mentioned only)
- Aspho Fields (First appearance)(Appears in flashback(s))
- One Day (Appears in flashback(s))
- Gears of War 2 (Mentioned only)
- Jacinto's Remnant (Mentioned only)
- Gears of War 3 (Mentioned only)