Katherine lost her parents when she was small as a result she can't remember who they were. When she heard about the legend of Toothiana, she had hope that with her baby tooth, she could remember them.
Katherine's adopted father. After the deaths of her parents by a terrible snowstorm, Ombric found her as a baby and decided to raise Katherine as his own.
From the first moment she met Nightlight, Katherine has been close friends with the boy. Katherine trusts the boy so much that she knows that she can trust him with her own life. In Toothiana: Queen of the Tooth Fairy Armies, Nightlight actually saves her from falling to her death. In Sandman, Nightlight and Katherine share their first kiss when Nightlight sacrifices his 'Kiss of Goodnight' in order to awaken her from Pitch's spell. It's implied that Nightlight and Katherine have begun to develop romantic feeling towards one another from that moment as The Sandman and the War of Dreams mentions that Katherine and Nightlight share a distinct happiness that only the closest of friendships have after going through a 'great change', Nightlight mentions that he's no longer afraid of the future as long as he has Katherine by his side.