M-kun and Ayumi, a brother and sister bound by blood and circumstance, find themselves alone in their shared home. Bored and restless, Ayumi starts to touch herself, her fingers exploring her wet slit as she imagines her brother's touch. Caught in the act, M-kun's initial shock gives way to a shared lust, and they tentatively begin to explore each other's bodies. Their taboo connection deepens as they give in to their forbidden desires, their bodies entwined in a dance as old as time.