Himari Kinoshita planned a hot spring trip with her younger brother as a final memory together, but this was no ordinary farewell—it was a calculated journey driven by twisted affection, designed for incestuous creampie encounters with a lesbian twist. Overcome by desire upon seeing his sister's naked body for the first time, the brother loses control and blurts out, "Sorry, Onee-chan! I'm gonna cum inside you!" That night, an unexpected turn unfolds—not through his actions, but hers, as the sister initiates seduction. A forbidden record of secret sibling incest, known to no one else, is thus sealed between them.