MiHoYo have been just the best storytellers I've seen in games in recent memory. The way they weave details in between seemingly unrelated story elements is crazy. Last event with the Perilous Trail was the exploration of a specific moment in history told through modern actors relaying their roles and interweaved with their own stories and personal growth. Irodori was a simple shoutout to the Rokkasen in Japanese history alongside the progression of Inazuma according to the history it was inspired from all while an underlying game-related story unfolded to set up for the future.
Now you have this one. This supposed island getaway roped in certain characters but played off like some kind of larping filler episode. The first 2 days were cute but not really anything groundbreaking. Kazuha's history we'd already known. Xinyan's too and she really didn't grow from her Domain. Instead we learned that she's really on top of things! 
But that all built up to Fischl's and pretty much the focal point of this event's story. Now the tools were all in place and we then had our surface level story: Fischl needs to learn to grow up but growing up doesn't have to mean abandoning your childhood fantasies. We learn here that she's actually a great storyteller. That's something of a comment on real life. Sometimes people around you can just be the least supportive people you could possible meet. But for those that rise above and push on sometimes they end up really successful. Maybe MiHoYo themselves were in this same boat. Game development isn't exactly a well respected field of work in the Chinese mindset after all.
This part of the story required our friends Kazuha and Xinyan. Kazuha also ran from his past but eventually overcame it and thanks to the islands he was able to make up for one of his regrets from running away. Xinyan had always been mocked for her career path but she realized they were the miserable ones since she was able to figure out what she wanted to do with her life. Put them together and you give Fischl a roadmap to figuring herself out.
I'm not sure they were going for this intentionally but the scenario between Fischl and Immernacht Fischl plays out exactly like we'd see in a Persona game. And the point is exactly what we'd see in a Persona game. (Persona 4 and 5 specifically where each of the characters was given their own world.)
Here Fischl is shown to have been denying the fact that she's actually Amy and that Fischl was a character in a storybook she read once upon a time and she's since assumed that identity and ignored her true identity. By doing that she fostered a shadow in her heart that behaves in accordance with her id and the worst of her reasons for hiding her true self.
In Persona if you continue to reject your true inner self then the shadow will expire and you end up lost.
I think that would be so much worse in Genshin because we have the hilichurls who are forever lost to the gnosis and ascension. It is possible based on the knowledge that the Fatui machine was trying to mimic Kusanali's power that the mirages represent a test of will and failing it could lead to becoming a Hylic person. (I don't know if that happened to the Fatui affected. 
)
But of course Fischl rose to the occasion and grew stronger for it. In Persona that would have meant the Immernacht Fischl would have become her persona but since that's not a thing outside of that universe what is meant to happen is that you accept your true inner self which we see in the cutscene. (I also love that Immernacht Fischl said Fischl was weak. Such a parallel with Persona.)
Also similar to Persona is the need for social links. In this case of course we have Kazuha and Xinyan not to mention Mona has been Fischl's friend since Unreconciled Stars almost 2 years ago. But it's her closest friend Oz that really pushed her to accept herself.
All of this is based on my theory that Oz previously the Archon Naberius is a loyal follower of the Archon Amy (maybe even in love with her) and as a result of the Abyss plot for her Oz decided to take action. He fostered the split identity of Fischl in her as a way to give her an anchor to this new human life she has because one day the Abyss will awaken her Archon self and without "Fischl" she may lose herself to the old Archon's power.
And that old Archon's story is on full display during this quest so I'll break that all down next time.
Tips and Tricks from a Super Casual Genshin f2p
