Warning: Per Wiki Policy, Fridge pages are Spoilers Off! You have been warned.
Fridge Brilliance
Toshiro's Persona, Ernesto, is named after Che Guevara, a revolutionary counter-cultural icon... and a mass murderer who launched a brutal wave of bloody repressions and genocides once he took power. Then you remember one of the Tyrants fought in-game is the Shadow Self of Toshiro, who represents Toshiro's belief that he ruined people's lives through his investigation of Nakabachi's corruption and blackmail, and the Phantom Thieves' Personas don't need to be positively portrayed Anti-Hero figures, with the likes of Carmen and Milady being outright villains. The designers did put Che's negative aspects into account — and provides reason why Salmael feared Toshiro standing up for himself, as it's clear Toshiro is so done with how his family treats him that he doesn't care if it destroys trust in the government, because to him, Yoshiki and Marie aren't worthy of trust anymore and Japan needs to face scandal now rather than let it continue to fester.
It could also represent the incident with Nakabachi, which was a Full-Circle Revolution to an extent: the students he encouraged to rebel ended up becoming oppressors themselves, harassing Nakabachi into insanity, then turning on Toshiro when they were punished for it. By making Ernesto his Persona, he's keeping these events in his mind to ensure they never repeat, while healthily coming to terms with them.
Take a look at the clock in the third Kingdom. It's stuck at 6:00: the exact time for Eri's accident. Once Toshiro saves Erina, it starts moving again: a sign he's moving on from his past.
Incidentally, the Phantom Thieves are pulled into Marie's Kingdom when the TV anchor says it is now 6 o'clock.
Unlike both Persona Q: Shadow of the Labyrinth and Persona Q2: New Cinema Labyrinth, where the truth only comes out at the end of their fourth dungeons, Tactica reveals very early that its world is a manifestation of Toshiro's mind, and who and what the bosses represent is known long before they're fought. This makes sense as both Q games' worlds were born from young teenagers in denial of their trauma, while Toshiro is a mostly well-adjusted adult. It makes sense that he'd be quicker to notice the parallels with his own memories, as he's already had years to figure his life out.
It's also explicit he was in the process of gathering his will to stand up for himself already; Salmael literally suppressed his memories to force the Kingdoms to be a Black Bug Room that destroyed a gathering will. Quite simply, we're actually watching a faster version of the Character Development Toshiro had already as his memories return, so he's not in denial of how screwed up his life his and he needs a change. Seeing elements of the Kingdoms that are that terrible simply remind him of why and he recognizes the distortions for what they are.
Shadow Toshiro is strange in that he continues to exist despite Erina being an early form of Toshiro's Persona. Toshiro even awakens to his Persona before the boss fight, and Shadow Toshiro still puts up an intense fight. Given the nature of the Kingdoms, it's very possibly that Salmael was hijacking or puppeteering Toshiro's Shadow, in the same way Ameno-sagiri and/or Izanami did with Shadow Teddie (another being that defies normal Shadow logic as Teddie is himself a Shadow).
Another possibility is that "Shadow Toshiro" merely is a fake cognitive copy of the real deal, in line with how the "Questions for Lavenza" Talk Event in the Velvet Train reveals that the various cognitive beings based on people Toshiro knew are actually "fragments of Salmael's own existence." This may or may not also explain why the second phase of the battle sees Shadow Toshiro morphing into a nightmarish version of Eri in stark contrast to most other transformed Shadows.
While it's possible that the reason Toshiro doesn't gain a thief outfit like the rest of the cast is because he already sees his usual outfit as one, there's actually another possibility. It's mentioned multiple times throughout Persona 5 and its spin-offs that the outfits represent a character's image of rebellion. In Toshiro's case, that image is actually defined not by an outfit but by another person: Eri, and by extension Erina. Also, if one looks closely at Toshiro's mask the one time it appears, they may notice that it matches pretty well with Erina's clothes. This raises the possibility that the reason Toshiro doesn't get any clothes to represent his rebellious nature is because Erina is already fulfilling that role and, following that logic, Erina's outfit is actually just a female version of what Toshiro would be wearing.
Toshiro's mask has only one eyehole, over the right eye. The same eye that Erina's hair is always covering and the eye that his friend Eri Natsuhara is implied to have lost after her accident. Since the accident also robbed Eri of her optimism and sense of justice, Toshiro's one-eyed mask could be an embodiment of that lost hope, and him using it to summon Ernesto is bringing that hope to life once again.
Why does Luca trust the Phantom Thieves to help her if Repaint Your Heart takes place during the Casino arc, when the group is hated by the public because they're believed to be murderers? She doesn't know that Akechi framed them, and given that he was the one who publicly claimed they were innocent on TV and that she had been watching them, seeing the one who vouched for them acting as a member (his look is pretty distinct) would've been enough proof to her knowledge that they were still doing good.
On New Game Plus, there's a very noticeable case of Gameplay and Story Segregation — you can buy weapons for Violet and Crow from Erina's shop although she has no idea who they even are as far as we know. Or, maybe not. Early in the game when Erina first strikes a deal with Joker, Morgana tells her that similar situations have led to new comrades before. Which member of the team became part of the group through making propositions? Akechi, not once but twice. It was after they defeated him in Shido's Palace that he realized the weight of the hurt he'd caused, saved them, and stuck a deal with them that they'd change Shido's heart in his name — this was when he firmly became an ally instead of an enemy. Then, he proposes to rejoin to stop Maruki, which is when he becomes a member for good — a comrade. They may have evaluated on this off-screen and told her about Akechi, and by proxy Yoshizawa once their recollection reached a later point. Erina may have dug up a few weapons lying around that happened to be their type and put them up for sale just in case Joker would find a use for them later.
Furthermore, Erina is just the "shopkeeper" for the weapons. The real supplier is Lavenza, who is more familiar with Violet and Crow.
Fridge Horror
Salmael in general is an entity rife with Fridge Horror. It's a deity born from humanity's desire to avoid conflict, and it's taken to trapping rebellious individuals in traumatic mental worlds to break their will. And Lavenza speculates that the only reason Toshiro wasn't broken instantly is because he had Erina, an early manifestation of his Persona. This means anyone without a Persona is doomed to be Mind Raped with no means of resistance, and given how long it's been around, Toshiro might not have been its first victim. The worst part is that, unlike Yaldabaoth (or even something like YHVH from Shin Megami Tensei), Salmael genuinely believes it's helping humanity, its attitude being more Condescending Compassion than malice. Morgana is rightly worried upon hearing this, as this makes it ironically even harder to reason with.
The clock tower that appears during the climax of Kingdom 3 is stuck at 6 due to it being the time where Eri was pushed in front of the subway train by Nakabachi. As mentioned in the above Fridge Brilliance entry, this was a metaphor for how Toshiro was trapped in that moment and how it was smothering his rebellious spirit. Now, remember that the Kingdoms were created by Salmael specifically to crush Toshiro's rebellious will and revolutionary spirit. Salmael, among several other more obvious things, was intentionally trying to trap Toshiro in that moment for the rest of his life just to make sure he didn't stand up to Yoshiki or Marie, who are horrible people that will likely screw over many of the citizens of Japan with that amount of political and monetary power. "Wants to rid the world of pain" my ass.
Yoshizawa at times reacts far more emotionally fragile than the others when knocked back by an ally, with one of the clips being her yelling "Please stop it!" in desperation. Considering that Sumire has anxiety and constantly beats herself up, it would sadly make sense for her to subconsciously assume the worst and react in such a way instinctively. Also, Futaba calls her by her code name if she's used in the main game, which she doesn't even get until after the truth about her is revealed, which adds another layer to how heartbreaking this is if you know the context.
