Even though I agree with some of your points, I also have to disagree with the background of Haru in "Secret". As you may know, he was chosen to only be a side character in the story, which we all know from mangas, manhwas etc., and in those, there was never an explained background about a simple side character.
The reason is, the writer never intended to make a big story about him, that´s why he also has no home. He is that guy who just fills the background scenes.
If you talk about after he came back as Baek Kyung´s friend, then I agree. At that point, he should have had at least a bit of background because he became an extra there.
Also, I can explain myself the open ending:
Haru disappeared, they finished the "Secret" Comic and went to the next. But she kept her memories, at least got them back when she saw the drawing, and then they found each other again.
The reason the writer wasn´t mentioned, he/she/them don´t know anything about the changes, because he/she/they maybe don´t even know his characters have an ego nor that the shadow exists. So Haru and Dan-Oh will find themselves always. Since they are somewhat connected.
To me, it made sense that they had an open-end like that since creativity has no end too and maybe there will be even more comics after. We don´t know. But we never questioned that before with side-characters.
Okay, so the point I tried to make clear was:
They are side-characters - main characters in the series - who try to change someone's fate. Still, they always continued being "only extras", and most of the time, extras don´t get their own end.
I hope you could follow up on my thoughts a little bit... Also, I recommend you to rewatch it, once you know the end, then you will see Haru a lot more often.
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The reason is, the writer never intended to make a big story about him, that´s why he also has no home. He is that guy who just fills the background scenes.
If you talk about after he came back as Baek Kyung´s friend, then I agree. At that point, he should have had at least a bit of background because he became an extra there.
Also, I can explain myself the open ending:
Haru disappeared, they finished the "Secret" Comic and went to the next. But she kept her memories, at least got them back when she saw the drawing, and then they found each other again.
The reason the writer wasn´t mentioned, he/she/them don´t know anything about the changes, because he/she/they maybe don´t even know his characters have an ego nor that the shadow exists. So Haru and Dan-Oh will find themselves always. Since they are somewhat connected.
To me, it made sense that they had an open-end like that since creativity has no end too and maybe there will be even more comics after. We don´t know. But we never questioned that before with side-characters.
Okay, so the point I tried to make clear was:
They are side-characters - main characters in the series - who try to change someone's fate. Still, they always continued being "only extras", and most of the time, extras don´t get their own end.
I hope you could follow up on my thoughts a little bit... Also, I recommend you to rewatch it, once you know the end, then you will see Haru a lot more often.
xoxo Lin