Rudeus Greyrat originated as a 34-year-old Japanese NEET, overweight and reclusive, evicted by siblings after refusing his parents' funeral. Dying while saving a teenager from a truck, he reincarnated with full memories into a fantasy world newborn, vowing to live without regrets. Physically, he had light brown hair, green eyes, and a mole under his left eye, reaching 175 cm as an adult. His eyes turned heterochromatic after receiving demon eyes from Kishirika Kishirisu. He wore practical gray robes in youth, transitioning to refined attire later. Temporary mana depletion during battles sometimes drained his hair color, which regrew naturally. Haunted by past failures, he consciously cultivated humility and self-awareness. He prioritized protecting family and friends with fierce loyalty, reacting violently to threats against them. Lingering traits included extreme perversion, leading to inappropriate advances toward females in his youth, though he remained exclusively devoted to his spouses after marriage. Pragmatic in combat, he preferred negotiation against superior foes. High-stress confrontations triggered trembling, while severe emotional shocks caused vomiting. Fear of repeating failures drove meticulous planning. Mastering language and literacy as an infant, he discovered silent spellcasting at age two, practicing secretly until an accidental reveal. At three, he apprenticed under the demon mage Roxy Migurdia, who helped him conquer agoraphobia during a pivotal horseback ride beyond his home’s gate. Defending Sylphiette from bullies at five marked his first deliberate defiance of past trauma; he later taught her magic, forging a deep bond. Sent at seven to tutor his cousin Eris Boreas Greyrat in magic and academics, he also instructed her swordsmanship teacher Ghislaine. A decisive dance at Eris’s birthday celebration averted her public humiliation. During the ensuing Displacement Event mana catastrophe, he and Eris teleported to the Demon Continent. Guided by Hitogami, he allied with Ruijerd Superdia of the feared Superd tribe, forming "Dead End" to rehabilitate Ruijerd’s reputation while seeking a route home. A critical mission failure—delaying aid for dramatic effect—resulted in a preventable death, instilling lasting accountability. His journey included obtaining Kishirika’s Foresight Eye for combat prediction and Clairvoyant Eye for enhanced sight. At thirteen, he violently reunited with his father Paul in Millis, resolving tensions through mediation. Eris then initiated a sexual relationship but departed without explanation, citing incompatibility. Her abandonment triggered years of erectile dysfunction and depression. Enrolling at Ranoa Magic University on Hitogami’s counsel, he researched the Displacement Event’s causes while masking depression. He dueled and befriended "Fitz," revealed as Sylphiette in disguise. Their rekindled relationship restored his health, leading to marriage. Rescuing Roxy Migurdia during a quest for his missing mother Zenith sparked romantic feelings, culminating in their marriage. A confrontation with Eris clarified their misunderstanding, making her his third wife. Later, he allied with the dragon warrior Orsted upon uncovering Hitogami’s manipulations, earning the title "Quagmire" as Seventh of the Seven Great Powers after defeating Kalman III. His magical capacity rivaled the Demon God Laplace. He achieved Emperor-rank in water magic and Saint-rank in fire, wind, earth, healing, and detoxification, favoring earth magic in combat. He pioneered silent incantation for attack spells and created original techniques like the nuclear-level "Explosion." He fluently spoke Human, Fighting God, Beast God, and Magic God languages. In adulthood, he fathered six children: Lucy, Sieghart, Lara, Lily, Christina, and Ars. He established a Sharia household enforcing strict rat extermination—a response to Hitogami’s plague attempt on Roxy. He died naturally at seventy-four, fulfilling his resolve to live without regrets.