Caules Forvedge, eldest son of the Forvedge family, was born as a backup heir and designated caretaker for his older sister Fiore. Fiore possessed exceptional Magic Circuits but suffered leg paralysis, while their father deemed Caules's magical capabilities mediocre and representative of the family's decline. This solidified Fiore's position as heir despite her limitations and assigned Caules to support her. He studied magecraft out of duty rather than ambition, gradually developing an appreciation for engaging with "absurd, scientifically impossible phenomena" through practice. He maintained a modern perspective, owning a computer, introducing Fiore to cell phones, and enjoying contemporary interests like video games and anime. Unlike traditional magi, he viewed magecraft as an accessory to human life, harboring skepticism toward the Holy Grail's ability to reach the Root. He prioritized his sister's potential revival over magical ascension if forced to choose. His pragmatic mindset included a willingness to kill Fiore in a hypothetical Holy Grail War confrontation to spare her lasting despair, reflecting a greater consciousness as a magus despite his self-perceived mediocrity.
During the Great Holy Grail War in Romania, Command Spells manifested on Caules upon arrival, compelling him to serve as Master of Berserker of Black against his wishes. Using blueprints provided by Fiore as a catalyst, he successfully summoned the Servant, later apologizing for inadvertently revealing her true name under pressure from Rider of Black. His relationship with Berserker involved mutual accommodation; he avoided forcing her into spirit form to respect her moods and focused on survival. Their interactions included discussions about her wish for a mate and his own uncertain wish, culminating in her gifting him a flower before destructively ripping others apart, reminiscent of her legend.
After the war, Caules assumed leadership of the Yggdmillennia clan and negotiated its dissolution with the Mage's Association. The clan's surviving members avoided execution largely due to his role in rescuing the Red Masters, particularly the high-ranking Clock Tower member Feend vor Sembren. As part of the settlement, he relocated to London under the Association's supervision as a de facto hostage, accompanied by Althea, who assisted with household chores and magecraft. Studying at the Clock Tower, Lord El-Melloi II recognized his affinity for Electricity Magecraft over his family's traditional arts, redirecting his focus with the observation, "Why are you studying this kind of Magecraft which doesn’t suit you? Your talent is much more suited to this, you know?" This pivot placed him in the El-Melloi II classroom alongside formidable peers like Flat Escardos, though Caules often expressed a longing for an ordinary life and discomfort with their intense personalities.
In the timeline of *Lord El-Melloi II Case Files*, where Yggdmillennia never existed, Caules enrolled at the Clock Tower after Fiore relinquished her role as family heir, becoming the official successor under Lord El-Melloi II's tutelage. A decade after the Holy Grail War, he collaborated with the Atlas Institute to develop "Codecasts," a fusion of magecraft and technology conceived from his original concept. During this period, he maintained ties with former Yggdmillennia members, including Lemina Eltfromm, whom he regarded as a younger sister. When Lemina sought his expertise against the Knight of the Round Table Percival in the Doubles Subcategory Holy Grail War, Caules pledged to supply tactical insights based on his past encounter with Mordred.