The Ark Academy, chosen as a model case for inter-species school integration, welcomed a new transfer student, Elliott Leukosia, a popular member of a mermaid idol group. Elliott, with her delicate appearance and shy demeanor, quickly became adored by her classmates. However, she had a problem. Due to the characteristics of her mermaid species, her body would soon masculinize. "I transferred here to get your help, coach..." With her developing body, budding breasts, and slender waist, Elliott, with her innocent eyes, pleaded for 'Assistance.' The homeroom teacher, torn between desire and ethics, couldn't refuse... The mermaid's 'song' permeated his consciousness. A mermaid idol surpassing the popularity of AKB48 and TWICE is born! With her clear singing voice, your baton will also reach a forte!