I should start by noting that I accidentally spoiled myself on Takuji being "plural" while reading this chapter, though it ended up being made extremely obvious by the end of chapter regardless of my being primed for it. And shout-out to Knurek who guessed this twist while reading Rabbit-Hole II and told me while I was writing this post. Nice catch!
In fact, this chapter suggests that a significant number of characters, including Takuji, Yuki, Yuuki, the Wakatsuki sisters, and of course Riruru, are inventions and/or alternate personalities of some central person, strongly implied to be Takuji himself. It also seems likely that Ayana is such a character, though her role is enigmatic.
The various effects employed in this chapter make it clear from the start that what we are seeing through Takuji's eyes is a greatly distorted reality: These include the buzzing sounds we hear, how certain words are omitted, and how people appear blurry to Takuji, presumably until his imagination fills them out, and the fact that Takuji constantly suffers from lost time. Moreover, he seems to have rewritten or repressed memories, believing his mother to be dead and seemingly not being aware that he has a little sister. And these delusions seems to have followed him for a long time, as we learn when he talk about his bullies at his previous school: Supposedly these not only stopped his train at one point, but also hid in his closet at night and watched him, neither of which seems remotely plausible.
I initially thought that Takuji's delusions merely involved people acting out of character, as appeared to be the case for Zakuro and the Wakatsuki sisters, the latter having at least one scene where it seemed that reality and delusion overlapped. However, events involving Yuuki, in particular his and Takuji's fight on the rooftop on the 14th, led me to consider if Yuuki was a delusion based on Yuki. That is to say that Yuuki might have been Takuji imagining himself being as strong as Yuki, considering how close Yuuki's name was to Yuki and considering how similar Yuuki and Takuji looks (everything but hair is the same).
It seems likely that Yuuki originated when Takuji was sexually assaulted by his bullies, at which point he (as Yuuki) fought back and somehow managed to subdue them. Though it could also be that he was never bullied by them in the first place, or to this extend, considering that at least some of his previously bullying was likely delusional.
And it was eventually revealed that the Wakatsuki sisters are unknown to everyone but Yuki and Takuji, which is also where I started cluing in on Yuki and Takuji being the same person, since they share that delusion. In fact, we get a lot of clues that Yuki is Takuji:
These include fact that Yuki witnessed Zakuro on the roof in Rabbit-Hole I, despite it being Takuji who saw that. There's the fact that Yuki is affected when Takuji's personality is dominant and vice versa. The fact that Yuki knew Takauji's little sister and her mother. The fact that both play the piano, and the fact that Takuji remembers information from the kind of books that Yuki reads, information that feels alien to Takuji. There is also Kimika teasingly asking Takuji if he wears stockings when she finds out that he has seemingly shaved his crotch, which may lampshade the fact that he does in fact do so as Yuki. And the fact that both experience lost time.
There is also Yuki's weird bedroom, which doesn't seem to fit in her house, but looks like something like a storage-room made into a makeshift bedroom. It could be one of those many hideouts that Takuji tells us he has been creating in secret places. And them being the same person also explains why Zakuro's phone was there and why Takuji's fingerprints were all over the place.
Eventually the fact that the three of them are the same person is straight up confirmed by Ayana, which raises the question of how can Yuki show up and witness (and seemingly survive) Takuji's suicide? Though everything does go to shit at that point. On the other hand, we also see the death of Yuuki, so perhaps the final scene of My Own Invention shows a metaphorical death of Takuji, the personality, leaving only Yuki.
And who are the sisters actually? We get a quite clear confirmation that Kagami is the rabbit doll, that we've seen a few times before, during the scene where Takuji "defiles" her. This also explains why Kagami constantly shows up from behind Tsukasa, who is probably carrying the doll in a backpack. Tsukasa, on the other hand, seems to represent Takuji's little sister, whose existence he has repressed all memories of. This is suggested in the scene where Tsukasa talks about getting a doll from her brother, a scene triggered by them seeing a rabbit-doll, which is apparently her dearest memory. It seems to be the same doll as Kagami and the same as the doll Zakuro throws off a building? It is also suggested by the fact that Tsukasa turns into a black hole in reality towards the Rabbit-Hole II, in line with how Takuji has repressed his memories of his sister. However, it is not clear what relationship the sisters have with Yuuki. Perhaps their final actions on the roof reflect something that happened between Takuji and his little sister, where he seemingly forgot to lock the door somewhere, allowing her to follow him.
There is also the question of the nature of Ayana. It seems pretty clear that she is also not real, though her relationship to the three personalities and her motives are all unclear. But considering the way she shows up and disappears, her knowledge of Takuji's personalities, and her intimate knowledge of what Takuji is thinking and intentionally forgetting, it seems likely that she is yet another personality.
However, she also says things like "In this setting, I am human" along with other statements that seem to imply that she is something other than a mere personality. I guess we'll see.
Interestingly, Ayana also tells Takuji that he will not be the one to reach the next world, perhaps suggesting that Takuji (the personality) does not survive this chapter, but that one of the other personalities do survive.
This all also made me wonder what the significance of the first chapter was, in which Zakuro seemingly saves Yuki from being in a coma. We are told then that Zakuro fell and hit Yuki, which killed Zakuro and hurt Yuki. Thus it may be that Zakuro fell and hit Takuji, not Yuki, who did note in My Own Invention that the girls fell right where he had stood moments before.
Moreover, Zakuro is aware that that Yuki is and is not the person she loves (paraphrasing: everything about this person has has changed and they are not in this world any more), and hints that the two of them visited an amusement park together. Neither Yuki nor Takuji did that as far as we know, but that leaves a third option who knew about Zakuro and whose whereabouts we know little about: Yuuki.
It seems possible that Yuuki was the one who took Zakuro to the amusement park, during some of all Takuji's lost time, and that he was the one she fell in love with. This may also explain why Zakuro kissed Yuki (goodbye?) at the start of Rabbit-Hole II. Though that might also imply that she was aware of Takuji's multiple personalities, since she recognized Yuki and yet did not act as if anything was out of the ordinary.
However, if Zakuro hit Takuji then that would imply that everything that happened after that was part of the dreamworld, which while not out of the question seems a bit extreme. A less extreme alternative is that Takuji survived his fall at the end of Rabbit-Hole II/My Own Invention, or that he never jumped in the first place, but instead collapsed due to his wound. In either case, I also suspect that the childishly drawn world Takuji sees, the End Sky, with power-lines and a sea, represents the view from their hospital bed.
There is also an interesting discrepancy that I noted, namely when Yuki talks to Kiyoshi. From her perspective, he asks her to attend a party as a "main attraction", which implied that something will be done to her. However, when we see the same scene from Takuji's perspective, Kiyoshi rather seems to want her as muscle in a fight. Not sure what to make of it, though.
So what's next? The obvious answer would be seeing the story from the point of view of one of the remaining personalities or invented characters, my chief guess being that Looking Glass Insects will be from Yuuki's perspective.
As a final note, Kamika quickly became my favorite side-character in this story. I got her ending first and to be honest I kinda liked that better than the true end to My Own Invention. Oh well, at leat she won in either case.
