The consequences of the Thieves' intervention in the plot will be far larger-reaching, and potentially catastrophic, than they initially thought.
By Stealing the Hearts of the Parisians, the Phantom Thieves have allowed Yaldabaoth to grow in power. At the game climax, this will ultimately result in Yaldabaoth being able to spread his influence to Paris as well as Tokyo, and manifest Mementos into reality there, as well. There is an in-universe reason why a lot of the ML cast is far worse than in canon.
And that is because Yaldabaoth is exacerbating their worst traits and negative emotions, as he knows that the Miraculous Bearers, and by extension Marinette, are one of the major bulwarks of hope; if the Bearers break, then there will be fewer to stand up against him when he rises. So he aggravates Mme. Bustier's worst traits, as well as makes the others more willing to believe Lila. After all, if Marinette can no longer do her duty, the people of Paris would eventually lose hope, and be more likely to fall to Sloth. Adrien ends up travelling to the Metaverse, and encounters his Shadow
And said Shadow is like Shadow Futaba: He is a representation of the rebellious and more proactive side Adrien has, as shown in season 1 when he tries to sneak to school and when he helped Fu. He helps Adrien realize that he always knew deep down that turning a blind eye to other crimes because it would be easier for him is wrong and that his fears of losing the few friends and freedom he has is allowing other people (like Lila and Bustier) to manipulate him into turning a blind eye to the harm they are bringing to his friends. This causes Adrien to decide not to be manipulated anymore and to fight for his friends and freedom, awakening his Persona. Of course, this could follow a very familiar pattern from Persona 5. Akira, Ryuji, and Ann all started their work as phantom thieves to put a stop to Kamoshida- who had given them all reasons to hate him personally, as well as out of principle. Yusuke gained his Persona to resist his abusive mentor. Haru joined the Thieves to change her father for the better and avoid the awful Arranged Marriage he was trying to set up. Seeing as rebellion is such a Running Theme in Persona 5, the narrative places a lot of importance on standing up to the people who hurt you yourself when possible- with the help of The Power of Friendship, of course. It would really fit the pattern to have Adrien finally brought into the fold once things involved his father- and, obviously, that would involve certain things coming to light for everyone involved. But even beyond Adrien's talents as a veteran superhero, the Palace itself will likely resist them otherwise. There is definite precedent for a Palace being constructed by multiple people’s distorted worldviews. After all, the entirety of Mementos served as a Palace for the masses, representing their Sloth in handing over control of their lives to those in charge. If the combined hero teams were to attempt a Palace based on the Agreste mansion without properly preparing, it’s possible that their strength would begin to drain the instant they started fighting. A Palace Ruler is already a force to be reckoned with because their belief that "I am untouchable!" becomes a source of strength for them. What would happen if Gabriel Agreste's belief that no one could interfere with his home… mixed with Adrien's belief that "No one is coming to save me… I messed up so badly that I drove all my friends away, and so now no one cares enough to help me"? Their combined disbelief in "heroes" being able to oppose Gabriel might result in an automatic De-power effect whenever the Thieves are detected in the Palace. In order to overcome that effect, the heroes would have to reach out to Adrien and convince him that he does have friends, and there is hope for him to escape his father’s grip. This might be a good time for our heroes, especially the ones from Tokyo, to consider the possibility that they may have been a little rough on Adrien in the past few months. In their understandable anger over the complete failure of his “plan” for dealing with Lila, they might have been overlooking a few signs that indicated that Adrien could relate a bit more to their tragic backstories than they might be comfortable with. Before the Phantom Thieves reach out to Adrien, they’ll encounter a few of his Cognitions.
After Hawkmoth’s identity is revealed, the Thieves would be quite suspicious of Adrien as a possible accomplice, but the Palace will soon put those doubts to rest by showing the emotional abuse the kid goes through. In addition, the Thieves might encounter some Cognitions of themselves before they leave, created from Adrien’s anguish and frustration. For example, Cognitive Akira and the Tokies could berate Adrien that “Someone like you doesn’t deserve friends!”, or Cognitive Kobra could tell Chat Noir that he needs to just shut up and do what Ladybug tells him. Everyone would know that these depictions weren’t objective, but even if Palaces don’t do “subtle,” they might give some valuable insight into how Adrien has felt for the last few months. We already know that even Gabriel is outdone in sheer evil by some of the previous Targets and especially Shido and his conspiracy. His stomach churned when he found out Lila has driven some of her former classmates to suicide, and he and Mayura are as horrified as the heroes at Okumura's mental shutdown, outraged at the thought of someone taking a parent away from their child. Also, the whole reason he wants the miraculous is to revive his wife, which is a far more benign goal than most of the other targets. And the Phantom Thieves will learn about this when they traverse his palace. Don't get me wrong, he's still an asshole, a terrible parent, and a supervillain and will need to be stopped. But stealing his heart and having him confess his crimes might cause as much damage as it would solve. Especially considering Adrien. His reputation was already on thin ice with everyone after the Lila fiasco, and this revelation would almost certainly lead to people thinking he was in on it. Hell, Marinette's first thought upon finding out Gabriel is Hawkmoth was that Adrien was Evil All Along. I think she's smart enough to know that even if they tell Gabriel to state that Adrien was unaware of his actions, a good amount of people will straight up not believe it and assume the same. He'd likely get shipped out to a boarding school like Chloe from the public outcry, losing all his friends. Worst case scenario, he ends up driven to suicide like Marinette was, only with no one to stop him. And that's not even considering the possibility of Adrien being a Sentimonster and the dangers of that fact getting out.
Adding to this is the fact that Hawkmoth and Mayura have tried to get the Phantom Thieves on their side before. Granted, that attempt was during the aforementioned akumatization of Okumura, and the Phantom Thieves rebuffed him before Okumura died. But again, that was before they actually knew who he was and why he did the things he did. Just look at how the Tokyo Team addressed Goro, and that was after he murdered Futaba's mother and Haru's father. (Granted, they haven't really forgiven him for what he's done even after acknowledging that Shido is just as, if not more, responsible, and it's all but stated that Haru and Futaba still hate him but Hawkmoth doesn't need to be forgiven either.)
And for why they would need Hawkmoth's help? The Butterfly and Peacock Miraculous of course. Like it or not, Gabriel and Nathalie have the most experience using them, and in a world of cognition, those two miraculous in particular will be immensely useful in stopping Shido.
Obviously, Gabriel will need to confess eventually, and I don't think things will ever be 100% the same with him and Adrien after all of this even before then, but even though it doesn't erase the many horrible things he did, Gabriel can come back from it.
Seemingly Jossed for Gabriel. Nathalie is still up in the air though, having had a Heel Realization without a change of heart and leaving for parts unknown.
Out of everyone, Akira is the one who mistreated Adrien/Chat Noir the most, managing to break apart his trust in Ladybug and pushing him out of the team.
And now that this has resulted in Adrien nearly getting killed by Shadow Gabriel and him calling them all out for their complete lack of regard towards his safety, Akira is going to have to reflect on his actions. And when he does, he’s going to realize that he had gotten so caught up in the idea of him being a better person than Adrien because of how they treated the situation of Lila bullying Marinette, he has been holding it against Adrien and antagonizing him because of it, ultimately becoming a bully himself. Of course, this is going to horrify Akira, and this, along with the fact that Adrien nearly died because of it, he’ll start trying to be more empathetic towards others, not letting his status get to his head and thinking of all possibilities, leading to the plan with Sae and Goro, him bonding with Goro despite them being enemies and his refusing Yaldabaoth‘s offer. Emilie Agreste is the Treasure of Gabriel’s Palace
Since Gabriel had turned to terrorism in order to heal her, it’s natural to believe that she would appear as the Treasure of the Palace, both in and out of the Metaverse. This will serve as an issue to the Thieves, as Emilie is on life support, so they are going to think of something to get her safely or if they don’t realize it before the heist, act quickly as soon as possible after they pull off the heist to get Emilie to a hospital before she dies.
