One day, Kotarou was fired from his job. He thought it would be a good idea to get a day job to make ends meet, but then he gets a call from his father and decides to work for the construction company that his family runs.

The next day, his father took him to greet the craftsmen on the job site, and he noticed a female craftsman with big tits among them. He looked closely at her face - it was his younger sister, Konoka.

"It's been a long time, you little-”

"Don't talk to me so casually. If you tell that we are siblings, you will get your balls crushed."

Konoka seemed to have adjusted well to the all-male environment. The most important thing to remember is that you can't get away with anything without a little help from your sister.

[From official site]