"Sweet Pool" is a psychological horror and romance manga that explores themes of identity, transformation, and the boundaries of human connection. The story centers on Youji Mizuno, a high school student who begins experiencing strange and unsettling physical changes. These changes are linked to a mysterious red substance that appears in the school pool, which seems to have a profound effect on those who come into contact with it. As Youji's body undergoes grotesque and inexplicable transformations, he becomes entangled in a series of increasingly disturbing events.

The narrative introduces several key characters who are also affected by the red substance, including Shuuichi Wakamiya, a reserved and enigmatic classmate, and Zenya Takashiro, a childhood friend with a complicated relationship to Youji. Each character's connection to the red substance reveals deeper layers of their personalities and pasts, as well as their struggles with isolation, desire, and the fragility of their humanity. The relationships between the characters are fraught with tension, as they grapple with their changing bodies and the emotional turmoil that accompanies their transformations.

As the story progresses, the red substance becomes a catalyst for both physical and psychological metamorphosis, blurring the lines between life and death, human and inhuman. The plot delves into surreal and often grotesque imagery, emphasizing the horror of losing control over one's body and mind. The characters' journeys are marked by a sense of inevitability, as they are drawn toward a fate that seems both inescapable and deeply personal.

"Sweet Pool" is characterized by its dark, introspective tone and its exploration of existential themes. The narrative does not shy away from depicting the visceral and unsettling aspects of its premise, creating a story that is both haunting and thought-provoking. The manga's focus on the interplay between physical transformation and emotional vulnerability makes it a distinctive entry in the psychological horror genre.