"Tensei Ōji wa Renkinjutsushi to Nari Kōkoku Suru" centers on Prince Wein Salema Arbalest, the second prince of the small and impoverished Kingdom of Natra. After dying in a modern world, Wein is reincarnated into this fantasy realm, retaining memories of his past life. Despite his kingdom's dire state, Wein is a shrewd and resourceful individual, possessing a sharp intellect and a knack for political maneuvering. Rather than relying on brute force, he employs cunning strategies and alchemy to navigate the complex political landscape and secure his nation's survival.

The story begins with Wein facing internal and external threats. Natra is a weak kingdom, surrounded by more powerful nations eager to exploit its resources. Wein's father, the king, is incapacitated, leaving Wein to manage the kingdom's affairs. Recognizing the limitations of military strength, Wein focuses on diplomacy, economic reform, and technological advancement through alchemy. He establishes alliances, brokers deals, and outwits rival nations, all while maintaining the facade of a carefree and incompetent prince to avoid drawing suspicion.

Wein's character is defined by his pragmatism and willingness to make morally ambiguous decisions for the greater good. He is supported by a cast of key characters, including Ninym Ralei, his loyal aide and childhood friend, who belongs to the Flahm, a persecuted minority group. Ninym's unwavering support and intelligence make her an indispensable ally. Other notable figures include Lowellmina Earthwold, a princess from a neighboring empire who shares Wein's cunning nature, and Falanya Elk Arbalest, Wein's younger sister, who becomes a symbol of hope and unity for Natra.

The narrative explores themes of political intrigue, economic development, and the ethical dilemmas of leadership. Wein's use of alchemy serves as a metaphor for innovation and progress, as he leverages scientific knowledge to create new technologies and strengthen his kingdom. The series balances moments of humor and lightheartedness with tense political drama, creating a dynamic and engaging storyline. As Wein navigates the challenges of ruling a weak kingdom, the story delves into the complexities of power, loyalty, and the sacrifices required to achieve lasting change.