Genkai Shachiku OL Wa Ashitate Senpai Ni Numa Ttemasu

The company the protagonist began working for upon her graduation was a so-called "black company." (A business that exploits its employees.)
The number of hours she works overtime every month nearly reaches the maximum allowed by the Labor Standards Act. However, to a 22-year-old office lady, it is too much.

Even so, she hasn't quit yet, thanks to Adachi-senpai.
Contrary to his looks gentle, the senpai, five years older than her, is a salesman who keeps rubbing off the company's clients the wrong way...