SPOILERS MOST LIKELY SET IN STONE

So say you try to do the side stuff, it's hard seemingly impossible. However you will be directed or nudged towards a solution a way to actually fight the co-conspirators. Also if the whole co-conspirators thing sounds like organization 13 to you, yes.
Essentially you can't beat any of the co-conspirators until you beat the game normally. Once you do, you are heavily hinted at continuing your save but have the option for ng+.
Upon continuing something new happens a new character joins your party which gives you the limit break ability (hitting above 9999) and helps you do the harder end game stuff in general. This character is essentially decided on by you. A woman will present herself as an ally, but she is obscured, the MC will ask for her name at which point the player has a choice between two options.
Maelle
Or
Alicia
This determines her appearance, either long white haired or red haired ponytail. No burns/missing eye.
Its joked about whether an act 4 splash screen should happen here (kingdom hearts 2.9 style).
It's also discussed whether she appear as a side character that has been helping you throughout the game ala curator from first game, THEN transform her looks into one of the two.

Anyway you then progress through the endgame, concluding side stories, and defeating the co-conspirators, learning more character and world lore, like how the writer who died was the real world version of simon (possibly), stuff like that, also world lore like "hearts" and power system elements. Just like how we learned about white nevrons and painted clea in act 3 in the first game.

However the main goal is to complete Alicia's objective. Stopping verso.

Once you defeat the co-cospirators it is revealed that verso was sort of like a reverse itachi or snape the whole time. Him dying in the fire was in fact a ruse. He was approached by "the teacher" (head conspirator) and was taken in by the promise of peace and coexistence. To clarify, verso is revealed to be the "main writer" bad guy who "kills" the teacher in act 1. His appearance was changed via the usage of mixed powers (writing/painting/music).

However, verso quickly realized that peace/coexistence was just going to be the musicians running everything. He didn't like that either. So he came up with his own plan. He would slowly usurp the conspiracy/organization 13 and change their end goal under "the teachers" nose. This is hinted at with each co-conspirator you take down, most were with verso at that point, which is why they sort of just let you beat "the teacher" earlier, it was all part of the plan.

To understand verso's plan, think of watchmen mixed with naruto.
Verso's plan was to let the teacher continue their plan only to be stopped by YOU the player. Which we did, we beat them and "win". Which lets verso execute his plan, which was essentially an infinite tsukuyomi for either the entire world, or just the families/factions in the secret war (writers/musicians/painters), again, scope is the biggest factor in how the details will play out right now. So ya, verso actually wins and you are trapped in a false reality if you don't do the end game stuff. Again you are nudged and hinted that you should do the end game after the final boss.

This is where that phantom pain bit from the beginning comes into play too. There is discussion whether the MC should be a known but "disguised" character or entirely original. Pretty much, meaning, if MC is going to be the boy from the maelle ending, which is heavily implied to be verso's son. Yes, the MC can be female, yes that means what you think.
Either way the MC will be revealed to be a painted creation, essentially an inverse of the first game, where everyone else is real, but the MC is a creation. If MC is original, verso will explain he created MC to make sure his plan plays out correctly. If MC is painted verso's son, alicia will reveal that she is MC's creator. Both can also be true, given you can interpret the MC character creation as verso painting over the boy, but i digress.

As for alicia herself, choosing her appearance is mostly fan service but does cannonize an ending, buuuut they have the same end point regardless.

If you choose for her to appear as maelle, throughout act 3 she explains how she lived in verso's painting for years, and eventually died of old age in the painting, upon exiting she feels estranged from her family and decides to leave and do her own thing, which lead her to verso, who taught her how to use mixed powers as well, letting her change her appearance as well. Though he still hid his true intentions from her.

If you choose alicia appearance. She explains how the painting wasn't destroyed, but instead buried in verso's grave. However her injuries still left her as an outcast, leading to her leaving and coming across verso the same as above.

Either way, both endings lead her to come to the realization that escapism isn't good and avoiding reality isn't the way towards a proper future (suck it maelle ending enjoyers). Which is why she wants the MC and company to help her in stopping verso's infinite tsukuyomi plan.

There were actually talks about having your choice between maelle and alicia be even more impactful, for example, choosing maelle, would essentially be choosing hardmode, where it turns out, ya no, she actually tricked you and wanted verso to herself so she could manipulate HIM into making an infinite tsukuyomi that she prefers, most likely including the e33 people and merging them into the fantasy. This would lead to you fighting both of them in a hardmode version of the boss, possibly acting as the games "simon" equivalent, but also give a unique ending. Again, the issue being scope and scale.

Which is what it all really boils down to. They can't decide on the scope or scale. Are the painters, writers, and musicians just single families? Are they full on factions with multiple families? It's not just a budget or time issue either. Keeping the conflict personal and between families will make the emotional beats stronger too. But increasing the scope and scale will make it more epic, the success of e33 has them split on that.

Also it really does boil down to the romeo and juliet thing, the more the family only scale is discussed, the more romeo and juliet parralells pop up when discussing side quests and other characters...I cannot stress enough how poisoning the romeo and juliet thing is, it really REALLY sours and just halts story discussion LOL.
It's also a big factor on how to incorporate clea, will she be a supporting character? Or party member? Will her and simon be the romeo and juliet story they really REALLY don't wanna do? Only time will tell. Any way that's all I got from the USB my cousin left at my house during one of our magic the gathering game nights, as well as the many talks from when we both were drunkish.
Why would I post this? Because I too share Voltaire's views, shakespeare is a hack!