Wow I think I've actually figured this out after days of headache. I'll start with what's most directly portrayed in the Highlight Reel. All the girls are not real, they are imagined by the members. They hold different meaning though.

 

Jungkook's girl is a replacement for Yoongi, his role model. She's calm, collected, and stops Jungkook from acting out of impulse (she first appears into Jungkook's life when Jungkook was speeding angrily down the hospital, he wasn't fully healed yet and this may further harm himself, she makes him stop in his tracks and momentary make peace with himself). Later on, when Jungkook's better (off the wheelchair, can walk with crutches), she reminds Jungkook of his good memories with Yoongi, whom he hasn't been thinking of for a while. Jungkook tries to dismiss this, and transfers his longing to the girl instead. When he's fully healed (physically), he readies himself to propose to the girl, but only to realise that she was never there. She made him love himself (prioritise healing his injuries before he can do something rash) (only wants to run in the direction his heart was turned - quote poster - rather than see if he's physically capable or not), then disappeared once Jungkook was ready for reality.

 

Yoongi's girl is a replacement for Jungkook. The girl, just like Jungkook, prohibits Yoongi from smoking by taking away his lighter; in return, Yoongi does music arrangement with her just like he does with Jungkook (YG & piano, JK & guitar). He doesn't dare to do these things with the real Jungkook, because he feels deeply guilty (as explained by a popular trend on twitter, it is likely that Jungkook got into the accident because he was saving Yoongi, according to the timestamp evidence of Begin & First Love) and believes that he brings misfortune to the ones around him (same words on his poster). The girl had helped him function better for a while, but he eventually realises (after that mysterious phone call, that I cannot explain) that this isn't right, that he shouldn't be running away from facing Jungkook, that he isn't at fault for the accident because Jungkook would do that in a heartbeat for any of his hyungs and that's his choice. Hence, he pushes the girl away from him and tells her to go.

 

Namjoon's girl is his old self. Well-mannered, law-abiding, clumsy, the ideal son in the eyes of the society. That had changed after he started to hang with his group of friends esp Taehyung (partying, vandalising, being chased down by police etc). He first sees her on 5th June (a few days before the fight happened), lent her a helping hand. After the group falls apart, he starts to follow the girl around, and ponders if he should approach her to give her the hair tie (this implies that he's considering to return to his old self), but eventually chose not to and gets off the bus instead (the bus is also a symbol of Namjoon distancing from the group, because the group has always been associated with trains). He sees the graffiti left by Taehyung and realises that all this while, he's avoided looking for Taehyung, telling himself that this isn't the right time, but it's only an excuse, because Taehyung isn't fine ('im fine' is actually 'save me').

 

Taehyung's girl is his old self. Misguided, going down the wrong path due to family issues and bad influences. He tries to be a Namjoon (his personal Guardian and Demian) to his old self, by stopping her from shoplifting (which was probably his first step down the wrong way). He tries to act like Namjoon (playing the same game), but eventually he still landed his old self in trouble. Instead of trying to run away like he always did in the past, this responsibility he felt for the girl pushes him to turn himself in instead, meaning that he's finally acknowledging that this simply cannot continue anymore and wants to fix himself.

 

Jimin and Hoseok's story is a little bit complicated, so stay with me. The girl is actually Jimin's ideal self. A happy, confident, and great dancer. Generally perfect. This is why Jimin cannot bring himself to look at her (he films her, but flinches away when she looks back at him), because he thinks she's everything he isn't. To become more like her, Jimin practises really, really hard, until he pushes his body beyond the limit and ends up getting hurt instead.

 

Hoseok's happiness is actually dependent on Jimin's happiness ("as long as you shine, I'm okay"). He's hence happy in the presence of the girl, because he thinks that Jimin would be happy if he was his his ideal self. However, because Jimin and the girl are essentially the same, when Jimin injures himself, so does the girl. Hoseok rushes to save the girl, running under the rain to send her to the hospital for treatment, when he realises that this isn't Jimin - that this isn't the Jimin that he knows and loves. That saving this girl wouldn't be saving Jimin, his friend whom he hasn't been seeing since the fight happened. This realisation makes him pause, and at this point, the girl doesn't exist anymore because her role is done.

 

Jimin watches his ideal self disappear/die. He's drenched in the rain, but slowly holds up an umbrella. As we know from the theories since HYYH, water is associated with dreaming (ie being detached from reality). Jimin has always been in the water, because he is chasing after an unrealistic perfection (the girl) all along. Now, he's finally facing the reality that he'll never reach his standard of perfect, and it's time for him to learn to be comfortable with who he is, rather than an unhealthy obsession over being perfect.

 

Finally, Jin's girl is a veil of comfort to rid himself from the guilt that he's the reason the group fell apart. The offers him a solution: Smeraldo flowers, "sincerity that cannot be delivered". The flowers will make him feel better about himself because he'll feel like he's apologised, when he hasn't done anything. On the day he was going to pick up the flowers, he was considering several outfits (all the casual, youthful kind). After he's put on a sweater and was pleased with how it looks, he saw a vase of white lilies (symbol of the OT7 friendship) being knocked over, and eventually changes into a proper suit (adultwear). This is his way of saying he'll fully cut ties with his younger self. However, at the end of everything, we see that Jin eventually stuck to his initial clothes - he's now comfortable with himself. I'll explain more about this later.

 

Now, how can all this be tied up? We need to start with why the fight started. As we can tell from HYYH Note, Jin had said something that triggered Taehyung's anger, hence resulting in the fight. I think Jin had said something like he doesn't want to hang out with the group anymore because he's a grown adult now and doesn't want to be associated with the acts that they do. This is probably Jin caving in to the societal pressure of people who don't abide by societal rules & expectations.

 

Moving on, as an overarching theory, what exactly is happening? I think there are two ways to explain it, and both explanations have been popular theories since HYYH (basically is this a story about Jin or is this a story about all 7 of BTS) (and no, I do not believe in the 'xxx died' kind of stuff).

 

The first theory, Jin is the only person and the other 6 are parts of him (refer to Dreamteller's theory). All 7 of them exist in a virtual world of Jin's imagination. Everyone has their own backstory (eg Hoseok and his mom abandoning him, Taehyung and his alcoholic father etc), except for Jin, who's there mostly as an observer. He's barely involved, and few is known about him (eg his job, family history etc). In the real world, Jin is maturing into adulthood, and he believes that he needs to detach himself from certain parts of him that shouldn't belong to the adult world (once again, this theory has been heavily discussed by The Bangtan Theory blog/tumblr). Hence, in the virtual world, Jin triggers the fight and that leads to the 6 other members experiencing what was shown in Highlight Reel '起' and '承'. To placate his sense of guilt, Jin resorts to the Smeraldo flowers, and plans on delivering it to the graveyard of his youth (ie the 6 members, the parts of himself that he plans to throw away as a cost of adulthood) in a proper suit and everything), but he eventually gave up on that plan. He righted the vase, meaning he wants to preserve his youth (OT7), and leaves in his initial clothing. This decision is that he wants to try and be comfortable in his own skin, and Jin's decision then has a butterfly effect on his virtual world (Jimin and Hoseok lets the girl/perfection die/disappear because she never belonged; Jungkook and Yoongi came to realise that being obsessed with replacements of each other isn't a solution; Namjoon realises that he doesn't want to become his old, obedient self again and Taehyung takes responsibility for his acts and tries to fix himself rather than insisting that he's fine; Jin's girl also dies in a car accident, so there goes his denial-solution). In the end, Jin chooses to love himself for who he is rather than become who he was expected to be, and he will continue into the next stage of life with every part of him.

 

The second theory is that all members are real actual people, it's only Jin centric because Jin's the first into adulthood and hence he's the trigger to many things. At the end, after the members are able to love themselves, they find their way back together again.

 

As you can see from the difference in length, I'm a lot more inclined to the first theory because that would explain why Jin's special role throughout all the album concepts. And also, '结' didn't even feature any other members (in a form that isn't a flashback), so it means that Jin's decision is the decision of everyone. Maybe the phone call received by Yoongi is actually a 'command' given by real life Jin, to tell him to come back to his senses, something like that. However, plot-wise, it's easier to explain the 7-friends theory, how they drop each other calls (especially Hoseok calling Seokjin to tell him about the car accident).

 

Overall, the theme is clear. Jin's narration is a very good summary. Everyone is bound to not love themselves at a certain moment. Hence, they choose to put themselves in a dream, a dream where life is beautiful, where they are happy. However, even in the dream they know, that this happiness is temporary and hence they are fearful, fearful of when this will end. They will eventually realise that this is false, and they're only closing their eyes from seeing reality. That they're afraid because they cannot love themselves for who they are. They are full of regrets, always thinking of what they'll do if they could turn back time (be the nicest person, return to a carefree time). But people must not focus on their past mistakes, they can only move forward by forgiving themselves, and accepting themselves to be who they really are.

 

Because there are places that simply cannot be reached no matter how hard you try. You can never be the perfect person you want to be. You cannot be flawless, cannot not have made mistakes. To recognise this and to love yourself as who you are, to be yourself and not who you're told to be, is not easy. This storm (not loving yourself and basically an internal crisis) is over, but another storm (pressure from society) is coming. But you will not back down, you will face it and live as the person you are.