The Characters of Thorn Jack: Finn Sullivan

(Slight spoiler alert!)
A liberal arts major at HallowHeart College, with an interest in photography, Finn Sullivan, 17-18 years old, was named Serafina by her biologist/artist mother, Daisy Sullivan, after the seraphim, the angels of love, light, and fire. In Jewish tradition, the seraphim act as guardians between the world of man and the world of spirits. 'Seraph' means 'to burn.'
Finn's father, Sean Sullivan, an Irish professor of world mythology and folklore, nicknamed Finn after Finn mac Cumhaill, a mythical hero and the leader of a band of warriors who guarded the king of Ireland. As a child, Finn mac Cumhaill was accidentally gifted with wisdom by a magical fish.
Finn's sister Lily Rose, whose suicide Finn witnessed, was a wild child and a ballerina. Lily Rose is the true object of Finn's quest.
Two of Finn's ancestors have also encountered the Fatas: Ambrose Cassandro, during the Renaissance, became a Jack (an immortal assassin for the Fatas), and Rose Govannon Sullivan, aka Jill Scarlet/Red Riding Hood, in the 1700s, in the Basque province near France, came from a family who hunted the more monstrous Fatas. She was made into a Jill (a female Jack).