"Mystical Prince Yoshida-kun!" centers on Yoshida, a seemingly ordinary high school student who discovers he is the reincarnation of a powerful mystical prince from a parallel world. This revelation comes to light when he encounters a mysterious girl named Aria, who claims to be his guardian and guide from the other realm. Aria explains that Yoshida’s past-life memories and abilities are essential to prevent an impending catastrophe threatening both worlds. As Yoshida begins to regain fragments of his past, he learns that his former self was a revered figure who wielded immense magical power and was deeply connected to the balance between dimensions.

The narrative unfolds as Yoshida navigates his dual identity, balancing his mundane high school life with the growing responsibilities of his mystical heritage. He is joined by a group of allies, including Aria, who possesses her own magical abilities, and several classmates who become entangled in the supernatural events. Together, they face adversaries from the parallel world, including dark entities and rival factions seeking to exploit Yoshida’s powers for their own gain. The story explores themes of identity, duty, and the clash between ordinary life and extraordinary destiny.

As the plot progresses, Yoshida’s powers grow, and he begins to uncover deeper truths about his past life, including the reasons for his reincarnation and the true nature of the threat he must confront. The series blends elements of fantasy, action, and school life, with a focus on character development and the evolving dynamics between Yoshida and his companions. The stakes escalate as the boundaries between the two worlds begin to blur, forcing Yoshida to make difficult choices that will determine the fate of both realms.