Born with the "Mortal Sin" skill of Gluttony, Fate Graphite is the central protagonist who initially appears as a weak and downtrodden youth. He is approximately sixteen years old and possesses a slim build with black hair and brown eyes, though his eyes are known to turn red when his skill's hunger becomes overwhelming.

Fate's background is one of hardship and rejection. After his father passed away, he was banished from his home village by its inhabitants, who considered his seemingly useless Gluttony skill to be a source of misfortune. Ostracized and left with nothing, Fate made his way to the royal capital of Seifort, where he struggled for five years to find work that would allow him to survive. Eventually, he was employed by the noble Vlerick family as a lowly gatekeeper, a position in which he endured constant humiliation and abuse from the three Vlerick siblings, who treated him as a slave.

The course of Fate's life changes dramatically when he accidentally kills a fleeing thief. This act awakens the true potential of his Gluttony skill, revealing its secret ability to permanently absorb the stats and skills of any being he kills. This discovery prompts him to seek out a proper weapon, leading him to a sentient black sword named Greed, who becomes his primary partner and guide. Greed helps Fate understand the double-edged nature of his power and together they form a formidable pair capable of rapidly growing in strength.

Fate's personality is a mix of deep-seated kindness and ruthless determination. Despite the cruel treatment he has endured, he retains a capacity for mercy and compassion, especially toward those who have changed their ways. However, he can become cold and utterly merciless when anyone he cares about is threatened, showing no hesitation in eliminating enemies to protect his loved ones. He suffers from a profound inferiority complex regarding his social standing and the nature of his cursed power, which often makes him oblivious to the positive regard others have for him.

His primary motivation is twofold. On a surface level, he seeks to grow stronger, partly to gain revenge against those who tormented him. More importantly, he is driven by a desire to become powerful enough to support and protect Roxy Hart, the holy knight who treated him with kindness when no one else would and who eventually took him into her household as a servant. He holds a deep, unwavering admiration for her and resolves to do everything in his power to stand by her side, even as he fears that his uncontrollable Gluttony could one day put her in danger.

Throughout the story, Fate's role evolves from a helpless victim of circumstance to a secret, powerful force that operates from the shadows. To conceal his identity while he is forced to hunt at night to satisfy Gluttony's endless appetite, he adopts a masked persona, often appearing in black clothing and a skull mask. He eventually leaves the Vlerick family to work for Roxy as a gardener, a position that brings him closer to his ideal. His journey sees him becoming a Holy Knight and later the head of the Barbatos family, all while uncovering a grand conspiracy that connects his own power, his family lineage, and the fate of his friends.

Key relationships define much of Fate's development. His bond with Roxy Hart is the emotional core of his journey; she is his love interest and his most cherished person, though he is slow to confess his feelings. He also forms a significant partnership with Myne, another Mortal Sin skill user who possesses the skill of Wrath. Myne becomes his traveling companion and mentor, teasing him often but harboring deep care and romantic feelings for him that she later confesses. His relationship with his sword, Greed, is that of trusted partners who bicker and banter, with Greed often serving as the knowledgeable but sarcastic advisor. He also gains a mentor and adoptive father in Aaron Barbatos, a seasoned warrior who teaches him powerful sword techniques and names him his heir.

Fate's personal growth is centered on his struggle to control his power rather than being controlled by it. Gluttony is an insatiable and uncontrollable skill with no upper limit. If its hunger is not sated for a period of time, Fate loses himself to a Berserk state where he becomes a nearly mindless, red-eyed predator driven only by the urge to consume. His development arc focuses on learning to manage this monstrous aspect of himself, shifting from using Gluttony for survival and revenge to wielding it as a tool to protect others and achieve a greater good. He seeks to overcome his cursed nature and find a way to exist without being consumed by the very power that makes him strong.

His notable abilities are entirely centered on his Mortal Sin skill, Gluttony. The primary function of this skill allows him to permanently absorb all the statistics and skills of any living being he kills, leading to a unique situation where his level remains at one even as his raw power continues to rise without bound. When he refrains from using Gluttony for too long, he enters a "Hunger Boost" state that powers him up but also threatens his sanity. To utilize the skills and stats he has absorbed, Fate wields the sentient sword Greed, which can transform into different weapon forms such as a bow or scythe, with each transformation typically costing a portion of Fate's own stats to activate.