This is the incredible fan theory I found; I would love to give credit to who wrote it, but I don't know who you are! Random ARMY, you have my respect for this~

"Jin is most definitely our central character here, and I believe that, in both videos, it's him reminiscing and trying to deal with the loss of his friends. There's a motif, especially in the teaser, of him filming and photographing everything that's also briefly present in INU, when the film projector projects the lily over his heart. It also says to me, though, that even in his scenes in INU, V was already dead. There were the six petals, after all, and there's no interaction with any of the group, just his memories of when they all used to spend time together. Though we don't actually see V's suicide until the teaser, I believe this points to Jin already having lost everyone.

It's pretty clear that in the "I Need You" MV, the only two members to survive (on screen) were Jin and V. The teaser picks up with V, dealing with the immediate emotional backlash of having killed someone. I would go as far as to surmise that part of what drove him to such a drastic action was him already failing to deal with the death of their other friends, and so seeing the man physically abusing the woman just pushed him over the edge emotionally. So, we see him trying to wash the blood off of himself and then calling Jin, knowing that he needs help to get through this. At this point, there's a cut, and I think that everything after this point in the teaser is after V has killed himself.

What we see next is V. He is alone and lying on the mattress in the empty swimming pool, when the rest of the group comes up and welcomes him, pulling him up. Jin is the only one not present, but when he appears, he's looking at them through the lens of a camera, as if he's watching an old video that he had recorded of when they were together. I think that everything he sees the group do here are memories he's having as he revisits the places they used to go, but throughout the video, his subconscious keeps subtly reminding him that they're not really there. Like other people have pointed out, there are parallels between the two videos alluding to the deaths of the members. We see J-Hope lying down with the same expression in both, Suga with the lighter, Rapmon with the lollipop at the gas station, Jimin shivering in the back of the truck (Jungkook is the only one without an obvious parallel, but maybe I'm just missing it? There is a slight parallel when he's walking on the edge of the swimming pool with his arms out, like he was walking on the edge of the ocean at the end of INU, but that's not directly alluding to his death, so I don't know.). Even in this first scene, we see him thinking about V's death with V standing up above the others overlooking the empty pool like he did the ocean, almost as if he's about to jump. We also see a moment of self doubt, as he looks up from filming the butterfly with a confused expression on his face, but as he looks and sees nothing but a plastic bag and the empty swimming pool, his memories are again triggered by the graffiti that V had left.

Next we see RapMonster writing "You Need to Survive" onto the mirror, another nudge from Jin's subconscious reminding him that he's the only one alive. Again, we see the video motif returning, as Jin sits watching videos of them together projected onto the storage cube. Jin pulls out a polaroid of the ocean, the exact same shot that's the very last thing you see in the INU MV, and the place where V died. He says to himself, "Should we go here," his hallucinations/memories tell him yes, and he continues on his journey.

We get more shots of him driving, carrying his memories with him. Again, photo motifs, and it's very telling that he's constantly seeing the group through the lens of a camera, a universal symbol for saving memories. He continues driving until we get to the gas station. Rapmon asks for the camera, and then takes a photo of Jin and Suga in the cab of the truck before tucking it away in the glove box.

When we get to the beach, the first thing we see is that same shot of the ocean that was in the photo once again, outlined by Jungkook's hand as he peers at the water. Jin is sitting in the truck, again with his memories, until they compel him to get out and go sit at the water's edge. He remembers having sat there, filming the water, as V looks over at the scaffolding and then back at Jin, a sad look on his face. Jin is too absorbed in his filming to notice V get up and head towards the scaffolding, only realizing it when he's almost to the top, at which point he turns the camcorder to film it. This part seriously gets to me, as, in my theory, it implies that Jin got to watch V kill himself. We see him watching V on the scaffolding through the camera, indicating that this is a direct memory, as opposed to the vague allusions of the deaths of the other members, which he did not witness directly. With everyone else already gone, their memories start yelling and motioning for V to come down, but he just gives Jin a sad smile and jumps.

After the credits, we're back with Jin in the truck, as he's remembering them all fondly, still in some sort of denial over all that has happened, but having reached the end of his journey. He pulls out the photo of himself and Suga that Rapmon had put into the glovebox, smiling until he actually sees it and realizes that it's just him, and that the rest of them truly are gone. This is when he stops smiling, hearkening back to the text that had flashed on the screen earlier, "You can smile as long as we're together." Jin realizes that he is alone."

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