perpetual rank-and-file employee; career non-promotee
Colloquial abbreviation of 万年平社員. Used humorously or self-deprecatingly for someone who remains a regular employee without ever being promoted.
He's been with the company for twenty years and has always been a rank-and-file employee who never gets promoted.
If you don't want to end up as a perpetual non-promotee, you need to produce more results.