Sonja Belikova is the second child in the Belikov family. She lives in Baia with her sisters, her nephew and niece, her mother and her grandmother. Sonja is currently working in a pharmacy in a town, as she is pregnant by a non-royal Moroi named Rolan Kislyak. She hasn't told anyone about Rolan, so her pregnancy is something of a mystery, which leads to Rolan later trying to seduce Sonja's younger sister, Viktoria Belikova. Rose Hathaway, however, breaks the two apart before Rolan can use Viktoria the same way he did Sonja.

In Homecoming, Sonja's child has been born; in a Q&A, Richelle announced that Sonja's baby was a girl named Katya. Sonja is ecstatic at the news of her brother's return, as well as the extremely likely case of Dimitri and Rose's future nuptials, as she is seen discussing plans with her mother and sisters.