Hi. I'm a lurker and I've only been here recently because of Season 4. I know this is probably not a new opinion but I just like to share what I thought anyways.

What happened to Haida is basically a condensed version of what happened to Retsuko, specifically at seasons' 2 and 3. Haida got entangled with a higher up and a way more succesful person (season 2: Retsuko falling in love with Tadano) and he also got into higher and more precarious position in the company(season 3: Retsuko became an underground idol).

The consequences of these strokes of luck are pretty similar to what Retsuko had gone through. Haida became a puppet and did things he normally wouldn't want to do. Remember when Retsuko was about to abandon the idea of being married; it was something she truly wanted but she let Tadano influence her into thinking she'll be ok not to be in one.

Also, Haida tried to push through with his window dressing so long as he manages to keep his position and his false sense of self-worth, even if it meant putting himself in danger. Retsuko in season 3 brushed off the threat given to him by his stalker and still wanted to pursue her idol career until she was almost killed. Both Haida and Retsuko wanted to go through with their stroke of luck no matter how dangerous it was.

In the end, I think it was an exploration on Haida's inferiority complex that's been a common theme to him throughout the series. And this season had to show how such behaviour's toxicity can and will totally ruin anyone.

And I guess this makes both Retsuko and Haida even since it was Haida who convinced Retsuko to keep her job and not resign to being a shut-in. Retsuko, in turn, saved Haida from his insecurities that was eating him alive.

I know Season 4 isn't regarded as a great season by the majority, but I still kinda enjoyed it. Idk.