The opening reflect the fact Retsuko is a day-dreamer!

I always found weird that overly happy background of Aggretsuko season one opening.

If it to think about, it does match the fact Retsuko was a day-dreamer herself in the final episodes.

She even says:

"If I've learned anything, it's that life doesn't go the way you expect.
There are surprises, good and bad, and sometimes you fall on your face. But even if it's awkward, even if it hurts, you keep moving forward because when you do, you're already a little bit stronger than yesterday."

It's ironic that several fans failed to realize it and had a lot of false expectations to the point that some were spreading lies about the show's outcome.