Saki, who became Hajime's new mother through his father's remarriage, is only four years older than him, and Hajime constantly feels intense desire for her youthful body and beautiful, voluptuous breasts. Hajime, a student in a university pharmacology department, secretly administers a compound he created using a certain substance, mixing it into Saki's food as an aphrodisiac. After several days, changes begin to appear in Saki's body. His young stepmother's body now craves him more intensely than ever. Driven by the drug into a lewd and euphoric state, Saki surrenders herself to Hajime daily, deepening their forbidden relationship further and further.