Kai and Lily

This is the relationship between the witches Malachai Parker and Lily Chamberlain.

Kai is Lily's adoptive older brother via Ben Chamberlain. They bond over old stories about Lily's father, and Lily even gives him his century-old toy soldier back. Later, Kai saves Lily from an attack on the compound.

History
After seeing what has happened to his vampires at the Abattoir, Kai ventured to the cemetery with the devil star, hoping to make Ben bleed and take his blood. When he arrives, instead of using the star on Ben, Kai throws the star at a witch in order to save Lily's life. He takes Lily and runs back to the Abattoir.

Trivia

 * Kai also saved Charlotte Marshall, Lily's mother, when she was a baby.
 * Lily's birth brought about a reconciliation between Kai and Ben.
 * They are both children of Benjamin Chamberlain.
 * Lily, though, is Ben's biological child while Kai is his adoptive child.
 * Kai was the only one outside of the family her parents trusted to know the truth about her despite later having his memories compelled away by Ben.
 * Kai was the second, besides Charlotte, of Lily's family to hold her following her birth.
 * Kai helped cover up Lily's "death".
 * Kai is also one of the characters who is connected with the Chamberlain Family as he is Ben's adoptive son and best friend, Charlotte's friend and savior from when she was a baby, and Lily's adoptive older brother/savior.
 * Lily freed Kai from the cell that her father was keeping him in.
 * Kai saves Lily but makes sure that she can't see or hear the violence taking place.