"In Another World With My Smartphone" centers on Touya Mochizuki, a teenager who is accidentally killed by a divine being due to a clerical error. As compensation, the deity offers to reincarnate him into a fantasy world with his smartphone, which retains its functionality and gains magical enhancements. Touya accepts and is reborn in a medieval-like world filled with magic, mythical creatures, and advanced technology.

The narrative follows Touya as he navigates this new world, leveraging his smartphone's capabilities and the divine blessings granted by the deity, which include enhanced physical abilities and proficiency in all forms of magic. His journey begins in the kingdom of Belfast, where he quickly befriends the royal family and other influential figures. Touya's unique skills and knowledge from his previous life allow him to solve problems, invent new technologies, and combat threats, earning him widespread admiration and recognition.

Throughout the series, Touya forms a close-knit group of companions, including several young women who develop romantic feelings for him. These include Elze and Linze, twin sisters skilled in martial arts and magic; Yumina, a princess with the ability to see people's true intentions; and others who join his party over time. Together, they embark on various adventures, ranging from exploring ancient ruins and battling powerful monsters to uncovering political conspiracies and thwarting the plans of antagonistic forces.

The plot is episodic in nature, with each arc focusing on a specific challenge or discovery. Touya's smartphone serves as a central tool, enabling communication, research, and the creation of innovative solutions to problems. The series blends elements of fantasy, adventure, and lighthearted humor, with occasional moments of tension and conflict. As Touya and his companions grow stronger, they uncover deeper mysteries about the world, including the existence of ancient civilizations and the true nature of the divine beings who oversee it.

The characters' interactions and relationships are a key focus, with Touya's charisma and kindness endearing him to those around him. The series maintains a balance between action, world-building, and character development, offering a straightforward yet engaging narrative. While the story does not delve deeply into complex themes, it provides an entertaining exploration of a fantastical world through the lens of a protagonist equipped with modern technology and divine favor.