Beginners Queen ~Jun ga Ryoujou ni Naru Made no Seichou Kiroku~

After losing both parents in an accident and finding life difficult, the older sister (Takagi Maya) dropped out of university to support her younger brother. Although she has no sexual experience, she became a prostitute to earn a living.

Her younger brother (Masumi Takagi), who knows nothing about his sister, is listening to the store manager's stories about his experiences with his regular prostitute during his break from work. The store manager shows him a panel of his favorite prostitute, saying that they are in the same situation and therefore compatible.

Looking at the panel, there was someone who looked exactly like his sister, whose stage name was “Jun,” the nickname of Masumia.

Masumi thinks there's no way his earnest and kind sister would do something like that. Believing there must be some kind of mistake, he begins to investigate and try to find out the truth.

[Translated from the official site]