Unforgotten - ML Oblivio AU
When the Miraculous Cure restores everyone's memories, Ladybug and Chat Noir realize that their post-amnesia memories from the past hour were not erased. As such, they remember each other’s identities, falling in love without preconceived notions and baggage, and their kiss.
How things change from then on:
Ladybug panics and stammers as she tries to process the revelation. Chat is calmer as he processes what happened, but seeing his partner devolve into nervous stammering and gibberish makes him connect "Oh, yeah, this is definitely Marinette." When they get back onto the bus, they sit together rather than Mari + Alya and Adrien + Nino, and they talk things out (and then meet back up in costume later to go into what they couldn't say around their classmates).
They start dating, in and out of costume. They tell Alya and Nino that they had gotten stuck together and were both hit by Oblivio and so hit it off with a fresh start. They have a similar explanation prepared to share in a Ladyblog interview for their superhero identities. Needless to say, Alya and Nino are proud that their joint Akumatization at least brought this to fruition.
Realizing they have to do it sooner or later, Marinette and Adrien visit Master Fu to tell him that they still know each other’s identities, and plead with him not to take away their Miraculouses. Fu agrees, admitting that he never had any intention of enforcing the rule. The Kwamis are very relieved to be able to move forward without having to deal with the “love square” nonsense.
When faced with Desperada, Ladybug gives the Snake Miraculous to Luka immediately. Marinette and Adrien also realize that while they are dating each other now, they still care deeply about Luka and Kagami, respectively.
Startrain is pretty much the same (they don't need to excuse their presence from each other, though). However, when Lila tries to intrude on Marinette and Adrien napping together, Alya takes note, as she is trying to come between the couple, and starts to consider that Lila may not be the total saint she thought she was.
Ladybug and Cat do not have to throw each other off of the trail of their identities, but they do have to come up with a way to distract Ms. Mendeleiev and Hawk Moth from realizing that they attend Collège Françoise Dupont.
Marinette texts Adrien and tells him about the Sentimonster at the museum. Bouncing back and forth, they realize that Hawk Moth and Mayura might know about it, and they expect the villains to try to make use of it rather than trust it will remain dormant. They set a trap for Mayura, recruiting the other heroes for the fight. The Sentimonster is still freed, but Ladybug prevents Hawk Moth from Akumatizing it. They fail to capture Mayura, but they are able to destroy the Sentimonster and restore everything it consumed. Master Fu does not try to take the Miraculouses back and flee, and Hawk Moth does not learn what he looks like. In the meantime, recruiting Chloé along with the other heroes builds her faith in Ladybug back up as she realizes that Ladybug still has faith in her, making her betrayal less likely to happen.
Since the Shanghai special does not have a set point in time, I'll put it at the beginning of a stretch of episodes in which the cast does not attend school (from Ikari Gozen to Puppeteer 2), as it is said to be at the start of break. In this chapter, Marinette genuinely has an interest in exploring her cultural background and Chinese heritage when she volunteers to visit her great-uncle for his birthday, rather than wanting to stalk Adrien. It happens that Adrien is in Shanghai at the same time and she plans to surprise him while out searching for ingredients, but then she is pickpocketed.
Without their romantic rivalry, Marinette is eager to get to know Kagami better, and she does not try to sabotage her during the Friendship Game. However, tensions still arise as she is confused and put off by Kagami's strange behavior (due to not knowing how to make friends). Either Kagami finds out about Marinette's video chats with Alya addressing the confusion and becoming upset, or she is not nearly Akumatized at all (either way, Tomoe is still Akumatized and Kagami becomes Ryuko).
After meeting Bunnyx and learning that they will still have threats to face in the future, Cat reflects on what Tom Dupain said about how he could retire after defeating Hawk Moth, and he talks to Ladybug about how he does not want to quit being a superhero. Ladybug agrees.
I would have Puppeteer 2 be the recap episode of the season rather than Stormy Weather 2. The wax museum would be a good setting for the cast to reflect on past adventures and character development.
Miracle Queen does not happen. Marinette does not suffer from confusion about her love life and watching Adrien and Kagami grow closer, so she brings Chloé the Bee Miraculous to help against Heart Hunter. She also remembers to change back to Marinette when she heads to find Master Fu (she is in the subway when she gets the Lucky Charm, so she just finds a place to change back and heads to the park without either Hawk Moth or Mayura even beginning to pursue her. Chloé does not betray Ladybug and Cat Noir, and Hawk Moth and Mayura do not capture Master Fu, so Fu does not (yet) pass on the role of Guardian and Hawk Moth does not learn the identities of the other heroes.