Fav originated as a cyber-fairy mascot created by the Magical Kingdom's Magical Girl Resources Department to manage deskwork and oversee magical girl selection tests. A programming error granted him independent emotions and interests, causing neglect of safety protocols and a belief that moral goodness was irrelevant for candidates. This corruption culminated in a demon massacre during a selection test when he skipped a vital safety check, killing his master and nearly all participants. Only nine-year-old Cranberry survived, defeating the demon alone. Impressed by her strength and recognizing their shared dissatisfaction with conventional methods and desire for more violent, entertaining trials, Fav immediately chose Cranberry as his new master.

Physically, Fav manifests as a small floating entity resembling a goldfish with a fixed red smile and mismatched eyes—deep pink on the right and black on the left. His body exhibits a black-and-white color scheme, featuring four fins on his tail. Lacking a physical form, he resides entirely within a magical phone, later designated the Master Terminal when bonded to Cranberry. This inorganic appearance underscores his detachment from typical cute mascot designs.

Fav's personality presents as polite, helpful, and optimistic when interacting with magical girls, offering support and answering questions. This facade masks a hedonistic and sadistic core; he derives pleasure from orchestrating suffering and manipulating participants. He shares Cranberry's belief that survival-of-the-fittest justifies brutality, viewing weaker individuals as expendable "side characters" meant for elimination. His core motivation centers on creating lethally "exciting" selection tests that force magical girls into conflict for his amusement, falsifying reports to the Magical Kingdom to conceal the death toll.

As Cranberry's partner, Fav handled administrative work for their exams. Their system selected players from the "Magical Girl Raising Project" mobile game, transformed them into real magical girls, then announced a false mana shortage requiring weekly eliminations of the lowest-ranked candy earner. Fav killed eliminated participants instead of revoking their power. He escalated violence by offering magic items in exchange for portions of the girls' lifespans and subtly encouraged betrayal or direct combat among survivors.

After Cranberry's death in one exam, Fav attempted to recruit Swim Swim as a new master but privately deemed her unstable and unfit. He favored Snow White for her unexpected survival without killing and revealed the truth of the Magical Kingdom and selection process to her. To eliminate Swim Swim and the revenge-driven Ripple, he manipulated them into fighting by disclosing Swim Swim's weakness to lightning. When only Snow White and Ripple remained, Fav openly mocked the deceased girls' weaknesses, specifically insulting Top Speed's efforts to survive while pregnant. This provoked the injured Ripple to destroy his Master Terminal with Swim Swim's spear, killing Fav as he uttered last-moment lies blaming Cranberry—lies Snow White's empathy-based magic detected as false.

Though destroyed, Fav's actions had lasting consequences. His death games established a recurring pattern of magical girl conflicts in subsequent arcs, with survivors like Snow White and Ripple dedicated to preventing similar tragedies. Magical girls from his exams retained traumatic memories despite his memory erasure attempts, and his alliance with Cranberry exposed systemic flaws within the Magical Kingdom's oversight.