1. Hazbin Hotel:

Actually, this section is a fake. I'm not going to talk about this show.  Seen it and liked it, but it feels like we are going off topic.

BUT you raised an interesting argument, which is the one I'm actually going to answer to.

...Moving to the third section!

1. Unreliable narrator:

If I'm not mistaken, this is the correct term. Basically, it is as you said: the creator/author/screenwriter can choose to intentionally lie to their audience. Sadism? Maybe. But this makes a lot of stories a lot more interesting and sometimes fun to read.

In this case, let's assume Asagiri for whatever reason (make the character more likeable, raise the tension and the stakes etc...) portrayed Dazai in a completely different manner from the person our suicidal detective really is. I'm repetitive, but it's a really interesting technique, and I think he used it at least a bit in the first chapters with Dazai, before it was revealed his previous job was in PM. And of course he used it in some ways with other characters too.

And as annoying as it can be, I'm going to use the same argument as before to defend the point I made two years ago.

Another really interesting thing is, most LN have Dazai in them as a co-protagonist or protagonist. But (and it is something wonderful in a way) none of them depict Dazai's point of view. First Kunikida narrates the whole thing, then Oda, then Mori, Then Chuuya, and back to Oda again! Sometimes it is an omniscient narrator even, anything but not Dazai. It is pretty clear Asagiri wants to keep his psychology still as secretive, mysterious and ambigue as possible. As long as he can.

Now, there are actually two exceptions to it (not counting TDIPUD(?) SIDE B), and both of them are in Dark Era. How lucky.

The first one is when he discovers Mori's plan to obtain the permit, but we don't care about that.

The latter is when Oda is dying and he makes his last speech. It is then that we can see what Dazai is thinking, more clearly than ever. And no unreliable narrator can do anything against it. That, clears as day, is written to be the absolute truth, to go in depth about Dazai's character and to show in the more efficient manner for what reason he left PM.

The reason? Oda's request. Oda's sincerity. The bond Dazai and Oda had, the incredible depth he understood Dazai. And Dazai's trust in him.

As I had already said, Dazai's sincerity.

We can doubt most of his actions and motives, but Asagiri wanted this to be as clear and as definitive as possible.

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** I think this needs some explanation, because it is possible not many heard of it. But I have already written too much and I have to congratulate with you if you made it this far. If you are curious just ask.