"Puru Puru Hearts" centers on a group of high school students who discover they possess unique abilities tied to their emotions, which manifest as magical powers. The protagonist, Aoi Hoshino, is an ordinary girl who stumbles upon a mysterious artifact that awakens her latent powers. This artifact, known as the Heart Crystal, binds her to a group of individuals called the Puru Puru Guardians, each of whom wields a distinct emotional power—joy, sorrow, anger, and love. Together, they must protect their world from the Void Shadows, malevolent entities that feed on negative emotions and threaten to plunge humanity into despair.

The narrative explores the balance between emotions and their impact on the world, as the Guardians learn to harness their powers while navigating personal struggles. Aoi, representing love, becomes the emotional anchor for the group, often mediating conflicts and inspiring her teammates. The other main characters include Ren Tachibana, whose anger fuels his destructive yet protective abilities; Yuki Mizuno, whose sorrow grants her the power to heal and empathize; and Haruto Saito, whose joy brings light and energy to the team. Each character’s backstory is gradually revealed, highlighting their vulnerabilities and growth as they confront their inner demons.

As the story progresses, the Guardians face increasingly powerful Void Shadows, each representing a specific emotional corruption. The battles are not only physical but also psychological, as the characters must confront their own fears and insecurities to strengthen their powers. The overarching plot involves uncovering the origins of the Heart Crystal and the true purpose of the Puru Puru Guardians, leading to a climactic confrontation with the source of the Void Shadows. Themes of friendship, self-discovery, and the duality of emotions are woven throughout the narrative, creating a balance between action and character-driven drama.