Wisteria was raised as an adopted child in an earl's family after losing her birth parents. From a young age, she secretly harbored feelings for Bright, her childhood friend from a ducal family who could not use magic. Wanting to be of help to him, she devoted herself to researching a mysterious underworld called the Predawn Realm, a place filled with a sinister miasma that is linked to the source of magic.

One day, Wisteria's younger stepsister Rosalie is selected to become the guardian of the Predawn Realm. The role is effectively a death sentence, as the guardian must enter the realm and never return. Devastated by this news, Bright begs Wisteria to take her sister's place, knowing that Wisteria is skilled with magic and possesses a natural resistance to the miasma. Wisteria realizes that Bright is in love with Rosalie, and heartbroken yet resigned, she agrees to become the guardian. She enters the Predawn Realm accompanied only by the sacred sword Sartis, a sentient weapon that has existed since the age of mythology and can speak. Sartis pities her circumstances and remains by her side.

Although Wisteria was expected to die alone in the Predawn Realm, she manages to survive with the help of Sartis. For twenty three years, she lives in complete solitude while fighting the monsters that inhabit the realm. Her physical appearance does not age during this time, so although she is now in her forties, she still looks as she did when she entered the realm at twenty years old. Back in her original world, she becomes feared as a witch.

The story takes a turn when a twenty two year old young man named Lloyd Allen Wruining arrives in the Predawn Realm. He bears a striking resemblance to Bright. He declares his intention to defeat Wisteria and claim the sacred sword Sartis, but after being defeated, he makes an unexpected request to become her disciple. Lloyd is revealed to be the son of Bright and Rosalie, making him Wisterias nephew without blood ties. His arrival forces Wisteria to confront her past and the complicated feelings she still carries.