Krulcifer Einfolk is a transfer student at the Royal Officer Academy, hailing from the Ymir Theocracy, a powerful northern nation. Her origins are unusual: she was discovered as a child inside a treasure box within a Ruin — an ancient, enigmatic site — and was adopted by Stiyl Einfolk, a noble of the Einfolk house. Raised as his daughter, she devoted herself to excelling in various disciplines, hoping to earn genuine acceptance from her adoptive family. However, her achievements often created greater distance, especially after she won the Divine Drag-Ride Fafnir in a tournament by defeating a rival whom her adoptive brother had previously lost to, inadvertently bringing shame upon him. Later, during an incident where officials again tried to use her connection to the Ruin, the site rampaged. Stiyl rescued her but sustained lasting injuries, and he subsequently distanced her from the family to protect her from further exploitation. Rejecting an unwanted political marriage, she fled the Ymir Theocracy and enrolled at the academy in the New Kingdom of Atismata, seeking autonomy and a life defined by her own choices.

In personality, Krulcifer is composed, witty, and self-assured, often recovering from embarrassment with a clever remark. She carries a cool, distant elegance, but beneath that exterior lies a direct and daring nature; she prefers to confront problems head-on rather than rely on others. This independence can lead her to undervalue her own contributions, yet she also displays a playful, occasionally mischievous side, enjoying teasing people close to her. She is notably sensitive about her smaller chest size, a subject that provokes open annoyance when raised. Despite her poised facade, she cares deeply about how others see her, a trait rooted in her childhood desire to belong to the Einfolk family. In matters of affection, she seeks to present her best self to Lux Arcadia without becoming possessive, showing maturity by accepting the presence of romantic rivals.

Her motivations evolve across the story. Initially, she is driven by the need for freedom from the political obligations of her homeland and a desire to uncover the truth about the legendary Black Hero, which is why she takes an early interest in Lux. As she deepens her bond with him, her priorities shift toward supporting his battles and building a future where they can stand together. Ultimately, she becomes one of his trusted partners, culminating in her marriage to him and her role as one of the five queens of the New Kingdom.

Krulcifer’s role in the narrative places her among the strongest Drag-Knights at the academy and a key ally to the protagonist. Wielding the Divine Drag-Ride Fafnir, she fights alongside Lux and other heroines against various threats. Her status as an Xfer — a being with a special connection to the Ruins — makes her a strategic asset, able to interact with and partially control Ruin functions. Over time, she transitions from a guarded transfer student to a confident co-ruler who has reconciled with her adoptive family and found belonging on her own terms.

Her key relationships are central to her growth. With Lux Arcadia, she progresses from a wary first meeting to a deep romantic bond. She initially asks him to pose as her boyfriend to avoid political pressure, but after sharing their pasts and confiding in each other, her feelings become sincere. She tutors him and supports his identity as the Black Hero. With Lisesharte Atismata, she begins as a love rival, but through forced cooperation and mutual respect, their relationship matures into close friendship and trusted comradeship. Her adoptive father, Stiyl, is a figure of both gratitude and pain; his sacrifice and later distancing shape her drive for independence, but they eventually reconnect. Her adoptive brother, Zain, represents the familial strain caused by her achievements, though that tension also spurs her to seek a path outside Ymir.

Her notable abilities encompass a broad spectrum. As an Xfer, she holds limited authority over Ruins, able to open doors and manage certain functions, though using this on a major door temporarily blocks her from doing so elsewhere. She possesses a high aptitude for Drag-Rides, enabling superior synchronization and combat performance. Even unarmed, she is a skilled martial artist who can throw trained opponents like Lux. Her marksmanship is exceptional, delivering high-speed precision strikes at enemy weak points. A signature Xfer ability is Full Connect, which links her nervous system directly to her Drag-Ride’s sensors, dramatically boosting reaction speed and manual control at the cost of sharing the machine’s damage. To stabilize this state, she underwent a process called Baptism under Queen Raffi’s order. Her Divine Drag-Ride, Fafnir, is a balanced machine excelling in offense, defense, and mobility. Its primary special armament is the Freezing Cannon, a long-range sniper weapon that fires ice projectiles durable enough to immobilize large Abyss creatures. Her accuracy with it makes her attacks extremely difficult to evade, though solid barriers can disrupt the freezing effect.