Sophia is a mermaid who is a member of the Black Fin Resistance.
Sophia worked at the Ostrokon, the library in Miromara, and lived with her parents and her little brother. However, the death riders came to her house and took her parents as she grabbed her brother and they hid in the garden. She managed to leave her brother in the safety of her friends but her parents were still missing. She, Fossegrim, Coco and a handful of ostroki formed the Cerulean resistance group, the Black Fin Resistance.
Sophia meets Serafina in the Ostrokon after Sera is captured in their net. After Serafina leaves to find her talisman, the BFR's headquarters are raided by Vallerio's Kobold goblins and most of the Black Fins, including Sophia, manage to escape. She then makes her way to the refuse dump north of Cerulea, where the Black Fins meet in a kelp forest and head to a safe house in the azzuros, the blue hills.
Sophia saves Serafina's life during the raid of Miromara's treasury after she is wounded by a speargun. The two mermaids swim to the reggia, Merrow's ancient palace, to hide but are cornered by a dragon that the death riders were housing in the ruins. They manage to slip through a crack in the floor and discover a tomb,without any bodies, that Merrow built in remembrance of her fellow mages. Serafina reveals the truth about the destruvtion of Atlantis and the hunt for the talismans and she later heads north with the rest of the BFR to their new base in the Kargford.
After Ling claims to have found the spy who Mahdi reported to Serafina and solves the "puzzle", Sophia owns up as she feels extremely guilty and confesses that she was the spy to Serafina. Shocked, Serafina sends Sophia to be imprisoned.