The protagonist, a 33-year-old man named Tenma, dies from overwork due to excessive gaming. In the afterlife, he encounters a goddess-like guide who informs him he will be reincarnated into another world after a three-month training period. This training facility is designed to help reincarnators adapt to their new lives, but Tenma's training unexpectedly extends for fifteen years. During this extended period, he diligently trains, leveraging his gaming knowledge to become exceptionally strong. Despite the prolonged stay, which initially causes him despair and loneliness, he emerges with peak stats and skills, ready to embrace his new life at the age of 14.
The training facility, a 100km circular island, offers various amenities and a dungeon for combat experience. Reincarnators can adjust their aptitudes and skills before training. Tenma's initial setup allows for a balanced approach, but he later learns he can acquire specific skills like Appraisal and Item Box, though these are not obtainable through standard training and must be innate. The guide, despite her seemingly casual demeanor and complaints about her job, facilitates the process, though she is clearly overwhelmed by recent issues with reincarnators dying quickly after arrival. A critical error in the system's time acceleration setting results in one hour in the real world equating to one year in the training facility, meaning Tenma spent fifteen years training in what felt like mere hours.
The narrative then shifts to the world of the Vinthizard Kingdom, introducing its royal family. King has five princes: the eldest, a popular 28-year-old; the second, a 24-year-old intellectual advisor; and the third, a 22-year-old popular with soldiers. The first prince's mother is deceased, and the second prince's mother, formerly a first concubine, is now the Queen. The fifth prince, Arganth, is 10 years old and his mother, a former princess from the Hollick Duchy, became the second concubine through political marriage. The fourth prince, Valdiack, is 14 and his mother, Freesia, is a baron's daughter with exceptional magical talent. Despite her high magic capacity, Valdiack disappoints his mother and the court with his reliance on dark magic and less-than-ideal swordsmanship.
Valdiack, feeling like an outcast, trains diligently with commoners and lower-ranking nobles, particularly enjoying sparring with Dean, a former adventurer. He struggles with direct combat, relying on trickery, which Dean encourages him to overcome. Meanwhile, the 10-year-old Arganth experiences public humiliation at an audience ceremony, leading to increased isolation and a cold demeanor towards his siblings.
Six months later, Valdiack, now 15, is arranged to marry the 12-year-old daughter of the Denset Duke, whose heir has died. As part of this arrangement, Valdiack, his mother Freesia, and a retinue including Dean and Freesia's family, embark on a journey for a formal introduction. During the journey, their route is unexpectedly changed to a dangerous path near a forest by a royal official, despite the protests of Freesia's father, the Baron. Freesia intervenes, agreeing to the new route, which turns out to be an ambush. Freesia reveals formidable fire magic, repelling an initial attack. However, the group is forced to flee into the forest from a large number of black-armored soldiers.
Inside the forest, they face constant danger from monsters and pursuers. Freesia's magic proves effective, but she is wounded. The group suffers casualties, including the death of Gar, who succumbs to poison. Dean is also poisoned and severely injured, losing an arm. Valdiack, despite his initial shock and grief, takes charge, demonstrating newfound resolve. He prioritizes survival and training, recognizing the need to adapt to his circumstances. Freesia, along with the Baron and other loyalists, sacrifices themselves as a diversion to allow Valdiack, Dean, and the scout Karsh to escape.
Three years pass in the forest. Valdiack, Dean, and Karsh survive, adapting to their environment. Valdiack develops scouting skills, Dean recovers and becomes stronger, and Karsh excels at resourcefulness. They face challenges from monster settlements and treacherous terrain. After a prolonged period of survival and planning, Valdiack, Dean, and Karsh decide to make a concerted effort to escape the forest.
The story then jumps forward an unspecified, but significant, amount of time, implied to be over a decade. Valdiack, Dean, and Karsh have established a life in the forest. Karsh disappears during a scouting mission, presumed dead. Dean falls gravely ill and eventually dies, confessing his love for Valdiack. Valdiack buries his companions and, with renewed determination, resolves to leave the forest. He encounters a woman named Lydia, who joins him, and together they embark on a journey, eventually becoming adventurers. Valdiack, now calling himself Valdo, and Lydia gather information about his homeland and eventually return, where Valdiack finds a new companion who resembles his mother.
