How does Zim and Perfect Nothing Dib’s relationship progress from enemies who haven’t seen each other in years to Zim wanting to help PN, to them developing feelings for each other? Who falls first and why? Do they try to deny or suppress it or not even realize what they’re feeling for a while?
The simplest way I can explain it is that Perfect Nothing is *Mopiness of Doom* with extra steps, after all the AU was born thanks to that episode. They miss the other, they actively supress the thought before giving in
Once Zim realizes what is really happening thanks to Gaz after she came to see him (to question his dissapearence, to explain him what has happend and then force him to help her with her brother), it becomes a situation where Zim is left with the "forced" task of reconnecting with Dib while Gaz searchs for an explanation by investigating the hospital, and a treatmeant for Dib if possible. Hence why Zim decides to infiltrate the Membrane Labs as an apprentice in order to live with Dib, decipher what goes through his head and an attempt to make up for the time lost
Little extra concept art that I did about this, Zim got sad that his previous attempts at trying to expose Dib didn't work out and at how Dib truly didn't want to aknowledge him ↓
I believe Zim feels both curiosity and guilt at knowing that his presence meant so much for Dib, after all Dib got depressed, went into an asylum and later realized that he had to be tortured so he could forget about him and move on, since otherwise he would refuse to do so.
As much as he tries to supress this feeling and convince himself that he's only doing this for Gaz, that he never cared this deep for his enemy, he can't deny that he misses him; Dib was the only constant in his life as an invader in earth, one that gave him a motive to conquer or even turn against the Irken system; a frienemy that understood him. Of course, Zim is unused to be treated with such peace and politeness from Dib, what is normal for him is fights or at least some form of friendly rivalry, so he spends his time trying to get a reaction out of Dib ("un-cooperative colleagues" doodle), get his attention by showing off or trying to help him in an obnoxious way; overall trying to de-brainwash him by doing things that the old Dib would have enjoyed or get angry at because he knows him that much. All in hopes that someday, he can get his Dib back, as rejects of society.
Dib on the other hand, is complicated. He first has to face the idea that his "childhood friend" didn't dissapear into thin air to never come back, he was already accepting a life where he would never see him return; the more quickly he forgot about him, the better. He's avoidant, he's polite yet not really wanting to tell Zim anything; he has this mess occurring inside him, like a scar that has been opened before it fully "healed". He reluctantly accepts his presence in the laboratories with a rather sanitized explanation from Zim and because he has no choice.
But he can't act like he doesn't know Zim so well. He keeps warning Zim about certain food options given in the cafeteria because of his specific tastes, he defends himself with memorized movements when fighting or arguing; it brings a weird sensation of normality when he is supposed to be normal already, and that slowly rediscovers those unresolved feelings he had for Zim (a friend, and it hurts).
They slowly re-build a weird form of friendship in the labs, going through horrible hours, heavy work, strict supervisors, and awkward social gatherings. They help each other with proyects, Zim learns some of Dib's health difficulties and how to aid them (at least as much as Dib will allow), Dib unconsciously searches for Zim's presence by glancing around; it's the heavy setting of lab work that makes their bond get stronger again.
This friendship grows in Dib, being the only thing that feels genuine in a life where the people that interact with him is out of pure interest or just coorporate bussines, and a job that although he does well, makes him feel deeply empty and unhappy. He realizes that he wants to keep Zim by his side, but not in the way he is. Speaking in weird ways, trying to convince him that he is indeed an alien and that their misadventures were real, no, he can't let Zim keep digging a hole of denial.
So, in an act of compasion towards him, and maybe even a love confession that is still surrounded by confused thoughts, he decides that he's going to cure Zim, so he can keep him by his side and live a healthy life as "perfect people of society". So you could say that Dib is the one to fall first, in a very twisted way. He doesn't want to risk losing Zim again because of him not fiting in society. ("Disaster date" drawing)
After that I'm still figuring out the following events to get through the disastrous climax and the healing arc, so this is all I can offer ( ◜‿◝ )♡ I hope my long yapping satisfied your curiosity
["Perfect Nothing" — Invader Zim AU]
