Fai D. Fluorite, originally named Yuui, was born a prince in Valeria alongside his identical twin brother, Fai. Their birth was deemed a bad omen, blamed for national misfortunes. After their father died and their mother took her own life, the king imprisoned the twins separately within a timeless tower—Yuui at the base, Fai at the top. The king later executed Valeria's entire populace before killing himself, leaving the twins as sole survivors. Offered freedom for one twin by Fei Wong Reed, Fai sacrificed himself to save Yuui. Fei Wong altered Yuui's memories, making him believe he caused his brother's death, and placed two curses upon him: one compelling him to kill stronger magicians, and another causing dimensional collapse. Fei Wong instructed Yuui to use Sakura's feathers to preserve Fai's body and assist Princess Sakura. Rescued by King Ashura of Celes, Yuui adopted his brother's name "Fai" and received the surname "Fluorite," eventually earning the title "D" as Celes' highest magician. Ashura placed a phoenix tattoo on Fai to suppress his magic growth and prevent the first curse's activation. Fai used one of Sakura's feathers to create Chii, an artificial being modeled after his mother. When Ashura transformed into a murderous monster due to his own magic, Fai refused to kill him, instead sealing him in eternal sleep. Fearing Ashura's eventual awakening, Fai fled to the dimensional witch Yūko Ichihara. Though wishing never to return to Celes, he joined Syaoran's group to traverse worlds. Fai initially presented a carefree, cheerful facade to conceal deep emotional trauma and self-loathing. He maintained distance, showing little regard for his survival, and teased companion Kurogane with nicknames like "Kuro-rin" to avoid closeness. He gradually grew attached to Syaoran and Sakura, breaking his vow to never use magic without his tattoo to protect them. During the Tokyo arc, Syaoran's clone took Fai's left eye—the source of half his magic. To save Fai's life, Kamui's blood transformed him into a vampire, requiring him to drink Kurogane's blood regularly. This intensified his guilt, making him colder and withdrawn. He addressed Kurogane formally to sever their bond, confessing he had grown too close. In *Spring Thunder Chronicle*, Fai and the group arrived in Kurogane's home world, Japan, after escaping Celes' destruction. Kurogane sacrificed his arm during the escape. Fai later relinquished his remaining magic to Yūko in exchange for restoring Kurogane's arm with a mechanical prosthetic. This act freed Fai from his curses and burdens. He reverted to his earlier demeanor, using playful nicknames for Kurogane and displaying genuine smiles. After Fei Wong Reed's defeat, Fai chose to continue travelling dimensions with Syaoran, Kurogane, and Mokona. Fai's magical abilities stemmed from his blue eyes, granting high-level spellcasting and an extended lifespan. His powers included dimensional teleportation, defensive shields, and regenerative vampiric traits post-transformation. The loss of his eye halved his magic, and he later forfeited all remaining power. His key traits—emotional resilience, self-sacrifice, and hidden perceptiveness—evolved from trauma towards acceptance and loyalty to his companions.