Liebe is a devil who originates from the lowest level of the underworld, a place where power is the only currency. Unlike other devils, he was born without any mana, making him an outcast and a target for relentless bullying and abuse from his stronger kin. His weakness made him a victim of constant torment until another devil cast him out through a barrier into the human world. Alone and severely wounded, he was found by a woman named Licita, who would later be revealed as Asta's biological mother. Licita possessed a unique condition that drained the mana from anyone near her, forcing her into isolation, but because Liebe had no mana at all, she could safely care for him. She took him in, treated him as her own son, and for the first time, Liebe experienced love and belonging. This peaceful existence was shattered when the supreme devil Lucifero attempted to possess Liebe. To protect him, Licita sacrificed her own life, fatally wounded by Lucifero, and sealed Liebe inside a five-leaf clover grimoire for his safety. This grimoire later chose Asta, another magicless boy, and became the source of Asta's anti-magic abilities.

Liebe's personality is initially defined by a deep and consuming rage. He harbors an intense hatred for all devils, holding them responsible for stealing the happiness he had with Licita. This hatred is the core of his motivation: to kill every devil, especially Lucifero. He is cynical, bitter, and emotionally scarred by a lifetime of abuse and loss, carrying a profound sense of worthlessness stemming from his origins as the weakest devil. However, beneath this vengeful exterior lies a capacity for deep loyalty. When Asta, during the Devil-Binding Ritual, fought him not as an enemy to be subdued but as an equal, and extended an offer of friendship, Liebe was deeply affected. Learning that Asta was Licita's son and that they shared the same experience of being outcasts despised for lacking magic forced Liebe to reconsider his purpose. His motivation shifts from purely personal vengeance to a shared goal with Asta. He begins to embrace a bond of brotherhood, fighting not just for revenge, but to protect Asta's friends and the human world.

Liebe serves as the anti-magic devil residing within Asta's five-leaf clover grimoire. For much of the series, his existence is the hidden source of Asta's power to nullify magic. His role evolves from a bitter, hidden entity using Asta as a tool for revenge to a willing and equal partner. After forming a true equal contract with Asta, they are able to achieve a synchronized state known as Devil Union, or Unite Mode, which merges their bodies and allows them to use the full potential of anti-magic. This partnership makes them one of the most formidable forces against the devils of the underworld. Liebe effectively becomes an unofficial member of the Black Bulls, playing a critical role in major confrontations against the Spade Kingdom, the Dark Triad, and Lucifero himself.

His most significant relationship is with Asta, whom he comes to see as his foster brother and closest ally. This bond is forged on a shared history of being powerless outcasts and is solidified by Asta's empathy and refusal to treat him as a mere tool. The memory of Licita is the emotional foundation of Liebe's character. Her unconditional love gave him the only period of peace he ever knew, and her loss is the source of his deepest pain and his fierce determination for justice. His relationship with other devils is overwhelmingly antagonistic. He views them with pure hatred, especially Lucifero, and his primary goal remains to eradicate those who wronged him and Licita.

Liebe undergoes significant development throughout the story, particularly during the Spade Kingdom arc. He begins as a being consumed by revenge and self-loathing, but through his partnership with Asta, he learns to trust, to fight for others, and to embrace a new family. His journey moves him from a hurt and vengeful entity toward one capable of loyalty and cooperation, though his underlying rage never fully disappears but instead becomes channeled into a protective purpose. His most notable ability is anti-magic, a power that allows him to nullify all forms of magic. Because he possesses no mana himself, anti-magic does not harm him, making him the only being capable of wielding it safely. When merged with Asta in their Devil Union, he grants Asta enhanced speed, strength, and the ability to erase even the most powerful spells. This unique power, born from his own lack of power, makes him and Asta an unprecedented threat to a world built on magic.