Wixoss Novels
The WIXOSS Novels are a series of novels written about WIXOSS by Fumio Futase. They feature a female main character who loses twice but finally defeats her rival and becomes a card to continue fighting. The second book ended with the main character meeting Cocoon, the Dark Lord of Atonement, an almighty being who holds dominion over all WIXOSS battles and the Ruler of White Garden. There are two books in the series, the second one being titled The Wings of Lamentation Encase the Dream of The Ruined Country. Chiyori and Ayumi Sakaguchi are both fans of the series, and Kiyoi Mizushima had taken an interest in it (despite denying it in front of Ayumi).
In truth, the books were written by Futase, who was previously a LRIG, to fulfill the wish of her previous Selector, who wished to become a great novelist. After entering Fumio's body, Futase drew inspiration from her experiences as a LRIG to write the series, including the concepts of punishment upon losing, rewards upon winning, and a being that oversees Selector battles (the character that makes up Mayu's name, 繭, means "cocoon"). However, Futase had recently ran out of ideas. Since a LRIG disappears when they stop being able to fulfill their Selector's wish, Futase became desperate, and currently wishes to become a LRIG again to hear the rest of the story from Mayu. When she fought Ruko, despite losing, she gained the idea of Level 5 LRIGs for a story idea. It is unknown if the novels continued after Futase and Fumio returned to their original bodies.