Despite being bullied, scorned, and oppressed all of his life, a 34-year-old shut-in still found the resolve to attempt something heroic—only for it to end in a tragic accident. But in a twist of fate, he awakens in another world as Rudeus Greyrat, starting life again as a baby born to two loving parents. Preserving his memories and knowledge from his previous life, Rudeus quickly adapts to his new environment. With the mind of a grown adult, he starts to display magical talent that exceeds all expectations, honing his skill with the help of a mage named Roxy Migurdia. Rudeus learns swordplay from his father, Paul, and meets Sylphiette, a girl his age who quickly becomes his closest friend. As Rudeus' second chance at life begins, he tries to make the most of his new opportunity while conquering his traumatic past. And perhaps, one day, he may find the one thing he could not find in his old world—love.

After the mysterious mana calamity, Rudeus Greyrat and his fierce student Eris Boreas Greyrat are teleported to the Demon Continent. There, they team up with their newfound companion Ruijerd Supardia—the former leader of the Superd's Warrior group—to form "Dead End," a successful adventurer party. Making a name for themselves, the trio journeys across the continent to make their way back home to Fittoa. Following the advice he received from the faceless god Hitogami, Rudeus saves Kishirika Kishirisu, the Great Emperor of the Demon World, who rewards him by granting him a strange power. Now, as Rudeus masters the powerful ability that offers a number of new opportunities, it might prove to be more than what he bargained for when unexpected dangers threaten to hinder their travels.

In the immediate aftermath of the mana calamity, Sylphiette finds herself teleported to the heart of the Asura Kingdom: the royal palace. Her sudden appearance accidentally saves the life of second princess Ariel Anemoi Asura, who has her sights set on becoming the ruler of the realm. Witnessing Sylphiette's talent with combat magic firsthand, Ariel recruits her as her bodyguard and right-hand woman, commencing their journey to power—which proves far more treacherous than first imagined.

After his relationship with Eris Boreas Greyrat reaches new heights, Rudeus Greyrat is ecstatic. Unfortunately, his joy is short-lived, as Eris suddenly abandons him to embark on her own journey. Believing that Eris has lost all interest in him, a heartbroken and depressed Rudeus sets forth to the Northern Territories. With his sole goal being to locate his mother on the vast continent, Rudeus wonders if persisting through daily life is worth the pain, falling into a robotic routine as he endlessly ruminates on his lost love. However, the dangers of the North soon prove that one cannot survive with a dulled mind. While on a quest with the party Counter Arrow, with whom he recently became acquainted, Rudeus has a brush with death—an experience that forces him to finally snap out of his despair. With his newfound teammates, Rudeus rediscovers the pleasure of daily adventuring and moves forward with his original goal of living his second lease on life to the fullest.