"Ecchi na Karada no Tsukurikata" centers on the life of Kouta, a high school student who struggles with his self-image and confidence due to his small, frail physique. His insecurities are compounded by his unrequited feelings for his childhood friend, Rika, who is popular and admired by many. Determined to change his circumstances, Kouta decides to transform his body and improve his physical appearance. He begins working out at a local gym, where he meets a mysterious and enigmatic trainer named Shizuku. Shizuku, who possesses an unconventional approach to fitness, agrees to mentor Kouta on his journey to self-improvement.

As Kouta progresses in his training, he discovers that Shizuku’s methods are far from ordinary. Her techniques often involve unconventional and risqué exercises that push Kouta out of his comfort zone. These methods, while effective, frequently lead to awkward and humorous situations, particularly due to Shizuku’s bold and uninhibited personality. Despite the challenges, Kouta remains committed to his goal, driven by his desire to win Rika’s affection and gain the confidence he has always lacked.

The narrative explores themes of self-discovery, perseverance, and the complexities of relationships. Kouta’s interactions with Shizuku and Rika reveal layers of his character, as he navigates the emotional and physical hurdles of his transformation. Shizuku, while initially appearing as a quirky and eccentric mentor, gradually reveals her own vulnerabilities and motivations, adding depth to her character. Rika, on the other hand, remains a central figure in Kouta’s life, though her feelings toward him are ambiguous, creating tension and driving much of the story’s emotional conflict.

The series balances comedic elements with moments of introspection, as Kouta’s journey is not just about physical change but also about understanding himself and his relationships with others. The dynamic between the characters, particularly Kouta and Shizuku, serves as the core of the narrative, blending humor, growth, and occasional moments of heartfelt connection. Through its exploration of fitness, self-esteem, and interpersonal dynamics, "Ecchi na Karada no Tsukurikata" offers a lighthearted yet meaningful portrayal of personal transformation.