A brother and sister living in a peaceful seaside village were famous for their closeness.
They'd been together since they were little.
The younger sister, Yumi, would follow her older brother, Akira, around.

Even after Akira became an adult and Yumi grew up, their relationship remained unchanged.
"They're like lovers with a big age difference," such was their closeness that people around them would joke about it.

But... in fact...
Although they were brother and sister, they were actually lovers!

One day, the older brother continued to touch her, and the younger sister's breasts had grown to the point where they were a living example of the phrase "I raised them."
Finally, he could no longer bear it, and late at night, the two of them were alone in his room...