妹バブ！ ～Lowな妹の癒やしおっぱいがスゴいので、僕の人生捧げます～

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.