(I think this is much better than my previous theory that probably had some inconsistencies or some gray or confusing parts. Geez, hopefully after posting this I can just chill my toasty buns.)
My final FUK U SIS, SEE YOU IN TEN YEARS input:
Okay, I believe that Johan at some point believed his feelings did not matter apart from his sister’s and this was his way of coping with his mother’s choice. For 10 years, this would feed his endlessly growing need to create omnipresent creations (e.g., thought control experiments, hive mind stuff, counterfeit schemes, etc.) to impose upon whichever unsuspecting individual he could for fun.
By the time Johan had grown up, he likely had conjectures that he was the one who was unwanted by his mother and was supposed to be left behind in the apartment from very early on and that’s partially why he was failing to become a complete monster.
He felt he was failing to become a complete monster, since he always fell short of becoming the ideal “Johan.” This was his aim in the first place to become “Johan” and never break the illusion, so he could satisfy being constituent-ally a human and a monster in one. Instead, he only succeeded in putting a monster and another monster on top of another monster in one.
Since he was also trying to figure out why he consciously gave up his identity/accountability in the first place, he presumed that he had to have done it because he was sent to the Red Rose Mansion, and Bonaparta had forced him to give everything up somehow.
His strange and unusual conclusion that he both stayed in the apartment and went to the mansion is impossible for one person to undergo. It also possibly suggests that he wanted to divert far more blame onto Bonaparta rather than his mother.
Johan could not figure out which memory belonged to which and at what point one memory began and the other ended. Just how he managed to lose that distinction entirely I’m not sure.
I will say it might have something to do with having a different purpose/reason for living before he was shot compared to the altered purpose/reason for living after he was shot. Tenma saving the boy suggested to him that he was possibly wanted and that he truly was “Johan.” I’m going say it’s Tenma’s action that altered his reason for being and gave him the strength to leave his sister alone for at least 10 years.
I think the eventual confusion in identity, memories, and experience comes more from the fact that Johan had simply forgotten that the whole planning of both he and his sister transforming into “Johan” thing all started initially as a coping mechanism with his mother’s choice, and the fact the twins could not see their mother anymore.
He believed that both he and his sister had no choice but to leave their mother, and he would have to become “omnipresent” in order to protect his sister from her trauma. Therefore, he was the one who superimposed his mother’s choice with the storybook with his sister with everything else that happened to him.
I think he absolutely refused to acknowledge that he created the situation on his own, so he tried to erase his own feelings and inputs that implied he had created the plan as a figment of his imagination. He effectively discredited himself and erased his own self including why he did what he did. Bonaparta would effectively become the nameless monster and he and his sister would be like “Johan,” which would be what he probably desired most of all.
It was all because Johan believed it was he, his mother, and his sister who were connected in Bonaparta’s plan that he wanted to wipe all actions, choices, feelings, and consequences of those three clean using the storybook because they “deserved” it from continually being oppressed by the eugenics experiments.
However, when Johan tried to leave the scenery of the doomsday with his sister, in actuality, he could not. He collapsed with his sister, and they were both susceptible to fatigue and weakness. It confirmed they were both unwanted and unwanted=weak in his psyche—he wanted to erase himself from that existence with his sister and find a purpose even though they were nameless but he never could.
This created a dilemma deep down in his own mind that once had the ability to distinguish between whether he was more human or a monster. To say the least, he wanted to disregard his mother’s choice altogether for their own good. However, he would attempt to completely conquer all unwanted things out of a deeply formed habit/desire to not appear weak.
Attempting to erase the feelings surrounding that moment, he effectively created a mental block later on that he struggled to take down himself. Johan actually had to fight his own mental block of his own construct in order to see the truth and wake up from his “dream.”
Deep down by his own standards, Johan probably thinks he is no good just like Tenma thinks he is no good.
I still contend that after being shot in the head, his sister forgetting him, and following the plan to kill the moment he “awoke” which continually erased his existence cemented his inability to wake up from his “dream,” and guaranteed he would never be able to recover the part of himself that he threw away/destroyed and labeled as non-important.
I think he realized his sister could not help him at a certain point, and he could not help her so he had little choice but to leave her. He would still be unable to remove the myth he created surrounding the two from when he was a child even as an adult. He could do very little to gain his sister’s acceptance or forgiveness of her own free will, which further disintegrated his will to live.
Despite believing he may have had a purpose due to Tenma saving him, Johan was so used to this feeling of not existing or not being whole without his other half, since he still had a natural compulsion to incorporate his sister into his plan to become “Johan” that he would not let go of no matter what.
It was because the plan itself was THE final sentiment/purpose that he believed existed within him and her even though Nina never had any desire to become a part of it in the first place. He seemed to derive comfort from the nameless connection of the distant past between him and her even though it was not pretty.
Nina would be forced to forgive him because they were at an extreme impasse. If she didn’t want to forgive him, she would never be able to overcome the inexplicable urge to kill him. I think Nina was the one who had to try really hard not to say FUK U BRO, SEE YOU IN TEN YEARS because she seemed to really think he didn’t give a crap about her.
P.S. I think Johan had actually tried to provoke Nina to kill him if only because Tenma was going to kill him. I think in a way Johan believed that since Tenma was going to kill him, it generally meant that Nina was not wrong to shoot him the first time around. Strangely enough, if Tenma had shot Johan and killed him, that would one and for all, in Johan’s perspective, wipe Nina’s hands clean.
Okay, how was that? I tried to incorporate as many different peoples’ views as possible.