"In Another World With My Smartphone" centers on Touya Mochizuki, a 15-year-old boy who is accidentally killed by a divine being due to a clerical error. As compensation, the deity offers to reincarnate Touya in a fantasy world while allowing him to retain his smartphone from his previous life. The smartphone, now imbued with magical properties, functions perfectly in the new world, granting Touya access to communication, maps, and other utilities despite the lack of modern technology.

Upon arriving in the new world, Touya discovers he possesses an extraordinary affinity for all types of magic, a rare trait in this realm. His journey begins in the Kingdom of Belfast, where he quickly befriends local residents and demonstrates his unique abilities. He forms close bonds with several characters, including Elze Silhoueska, Linze Silhoueska, Yae Kokonoe, and Yumina Urnea Belfast, who become his companions and allies. Each character brings distinct skills and personalities to the group, with Elze excelling in physical combat, Linze specializing in magic, Yae mastering swordsmanship, and Yumina displaying a natural talent for divination.

As Touya explores the world, he encounters various challenges, including political intrigue, ancient ruins, and powerful adversaries. His smartphone proves invaluable, allowing him to solve problems creatively and gain an edge in battles. The narrative frequently blends lighthearted moments with action and adventure, as Touya and his companions travel across different regions, uncovering mysteries and aiding those in need. The story also delves into the world's lore, revealing connections between ancient civilizations, magical artifacts, and the divine beings who oversee the realm.

Throughout the series, Touya's relationships with his companions deepen, and his actions often have far-reaching consequences, influencing the balance of power among nations. The narrative maintains a balance between episodic adventures and an overarching plot, with Touya gradually uncovering the true purpose behind his reincarnation and the role he is destined to play in this new world. The series concludes with Touya and his companions continuing their journey, leaving room for further exploration of the world and its mysteries.