General
- As long as Marinette and Adrien wear their Miraculous, they're immune to being affected by akuma. Without them however, they're fair game. This was eventually deconfirmed by "Cat Blanc" and "Ladybug" — it's their personalities that make them so hard to akumatize.
- Fans have already decided that if they ever do get akumatized, Adrien becomes Cat Blanc, a white Palette Swap of Cat Noir, while Marinette becomes "Miss Fortune," who usually looks Ladybug with the black and red switched, similar to Antibug (though occasionally her costume is all black, but with the spots a darker shade). Cat Blanc became Ascended Fanon in Season 3. Marinette, on the other hand, has been nearly akumatized on several different occasions, none of which would have been named "Miss Fortune". Since it's established canon that the same person can be akumatized into multiple different forms, this one will probably stick around until the series finale.
- Adrien's parents were his and Marinette's predecessors as Miraculous holders, usually but not always with one of them having the Peacock. Gabriel Agreste was confirmed to have the Butterfly Miraculous, but as Hawk Moth, he's not exactly a "predecessor" to the heroes. Emilie, meanwhile, did have the Peacock Miraculous, and while it hasn't been shown what she did with it, it's the reason she's missing in the show's present day, as the Miraculous was damaged and put her in a coma.
- Can the Miraculous Cure revive those killed during an akuma attack? Canon is extremely unclear on this. The heroes consistently try to save people from dying, but that could be because they want to spare people the experience as easily as because they won't come back. Cat Noir's accidental killing of Uncanny Valley in "United HeroeZ" is treated seriously and her subsequent revival not taken for granted, but this could be related to the fact that she's a robot, plus the specials are dubiously canon in various other ways anyway. And there have been multiple disasters that, realistically, could not possibly have had zero casualties — unless the writers declare that they did. Ultimately, it's down to the individual fan to decide what they think about this one.
- Once both Unification and the Wish had been revealed, most fans assumed that using the Wish would involve a unified transformation with both Miraculous. The Season 5 finale showed that using the Wish involved an entirely separate procedure of having the kwamis take their true forms and fuse directly, with the Miraculous only being involved in that they are necessary to give kwamis orders.
- Marinette's parents will eagerly act as Parental Substitute figures for any and all of her peers that need it.
- Due to the show's Strictly Formula nature, Ladybug always summons a Lucky Charm before the battle ends, which she throws into the air to summon a World-Healing Wave of miraculous ladybugs. Many fans imagine that, if a battle were to end without a Lucky Charm being summoned, Ladybug could still summon the ladybugs by throwing her yoyo instead. Canon is inconsistent about this — "Weredad" in season 3 shows her summoning the ladybugs (offscreen) without her Lucky Charm, but "Destruction" in season 5 hinges on the fact that she can't summon the ladybugs if the Lucky Charm is taken away. It's possible to Fan Wank up a system that allows both of these scenes, but the intent seems to be that the Lucky Charm is required and "Weredad" was an error.
- A somewhat popular one is the theory that Marinette's parents know that she is Ladybug but are keeping it to themselves for some reason. This has died off a bit in later seasons where both have been akumatized and have shown no sign of knowledge of their daughter's secret identity while transformed, but has not gone completely away.
- Marinette is commonly seen as bisexual due to some of her interactions with other women, especially Alya, Kagami, Clara and Zoé.
- Plagg has lost several Cat Noirs prior to Adrien to suicide that started as self-harm (how many varies depending on the work/author) and Adrien is well on his way in following in his predecessors' footsteps because of how terrible his life is.
- After "Guiltrip" it became a common interpretation that Adrien has some level of suicidal thoughts, as when he is infected by the bubbles he tries to use the cataclysm on himself.
- Many people believe that Adrien also has a crush on Marinette but is oblivious to his own feelings.
- Since Adrien is a model and his father is a control freak, many people assume he is on a restrictive diet. Just how restrictive it is depends on how much any given writer wants to play it for angst, from turning down extra pastries to outright starvation or developing an eating disorder — or for laughs, have him actively seek out extra pastries and taunt Gabriel about it. In Real Life France, there are actually laws about models maintaining a healthy diet, even requiring a doctor's certificate to prove it, while in the actual show, no special attention is called to what Adrien eats, and he has no trouble getting snacks for Plagg — so overall, it's not a particularly plausible postulation.
- Some fanworks depict Adrien as an anime fan.
- It's been theorized since Season 3 that Adrien is secretly a sentimonster, and that creating him is what put Emilie into her magical coma. Hints to this end have been dropped like candy, and Season 5 would confirm that Félix and Kagami are both sentimonsters themselves, and while Adrien himself still hasn't been confirmed, it's been suggested so heavily that it would have to be a deliberate Red Herring to lead to any other conclusion.
- There are several fans out there who believe that Hawk Moth can pull a full-on Villain Override of his akumas, though the evidence that he's able to do this is fairly spotty in canon.
- Many fans believe that should Hawk Moth get the Ladybug and Cat Noir Miraculous and make his wish to revive/wake up Emilie, Adrien or Nathalie would be the one to die/fall into a coma in her place. In the Season 5 finale, it was shown that Gabriel could choose the cost of his wish — while the exact requirements of the "balance" aren't poked at too much, since he says "read my soul" and sacrifices himself, it's at least clear he wouldn't be caught by surprise.
- It’s a frequent idea that Hawk Moth avoids evilizing particularly dangerous people, such as violent criminals, as a mixture of him having standards and pragmatic concern for his own well being. This has somewhat died off in later seasons as his schemes have become more destructive and risky, up to and including akumatizing an already existing supervillain.
- Gabriel can be cowed by Adrien by the latter threatening to dye his hair into a gaudy color, often a shade of green. Though, with the revelation that Gabriel used to be a punk with a purple mohawk, it's left up in the air on whether he would've reacted at all
Other
- Nathaniel and Juleka commonly have parents who are to at least some extent neglectful and the former frequently gets Abusive Parents, with the bonus of a mother who uses her position as a social worker to make sure they get away with it, even if the abuse is to the point of open wounds or near starvation; this state of affairs is never received well by the rest of the class, who get fiercely protective of the redhead. Eventually deconfirmed for Juleka whose mother, Anarka, is loving, if eccentric, while her father, originally absent in her life but showing himself to be fairly attentive when he does enter it, is Jagged Stone.
- Gina and Rolland Dupain are commonly interpreted as divorced due to them seemingly not being together anymore but that isn't made clear in-canon.
- Ever since "Timetagger" revealed that the Hawk Moth of the future is not Gabriel Agreste many fans immediately jumped on the idea that it is Lila Rossi. This has been further implied in "Revelation" where Lila discovers Gabriel's secrets and plans to steal the Miraculous away from him, and finally confirmed in "Re-creation" where she recovers the Butterfly Miraculous after it is lost in the sewers when Ladybug knocks it off of Gabriel.
- Since even before Zoé was introduced she was commonly seen as a lesbian. This only grew stronger when the episode was released with tons of Les Yay between her and Marinette. Zoé being attracted to girls and to Marinette specifically would eventually be confirmed in Season 5.
- After "Guiltrip" revealed that Rose had an unknown illness many jumped on the theory that the reason that Future Alix was so protective over Rose's unicorn plush is that by that time Rose had died to her illness.
- Regarding the contest in "Stormy Weather", several fans have assumed it was rigged in Mireille's favor (typically for the drama making great ratings), judging by the way Alec is quick to rub her victory in Aurore's face and the lack of Aurore balloons being sold compared to Mireille balloons. The aforementioned rubbing it in has led to it generally being assumed that he was involved in rigging it for some reason; Mireille, conversely, is generally (though not always) assumed to have been completely oblivious to it, since she and Aurore are shown to be friends in later episodes.
- Among the friend group of Marinette's girl pals, Mylène tends to be the only one consistently written as straight, with the others tending to be some form of either bisexual (Marinette, Alya, Rose) or lesbian (Juleka). Alix's sexuality varies before and after the Word of God that she's Aromantic but Alix typically sticks to the pattern of Mylène as the token straight friend with Alix being some other sexuality than heterosexual.
- Marc is often written as either non-binary or gender fluid.
- Prior to their father being established to be Jagged Stone, it was common to have Luka and Juleka be half-siblings with different fathers. This became a bit less common after the show established who their father is and retconned an original Word of God that Luka was older to having the two be twins, though it is still not unheard of. In these later scenarios where the idea of the two being half siblings is retained, Jagged generally remains Luka's father.
- Like many series, fan theories on how long the series takes place in the world exist outside, and against, any statements in series about it. Typically fans will assign the course of the show to take place over the course of at least one year within the first 2 to 3 seasons, often covering the events of later seasons in a second year, where the show firmly states that the first 5 seasons take place within a single school year. Despite this, you do not typically see these fics address the fact that the classrooms should have changed, as shown at the start of the series in Origin.
- While Chloé shows an obsessive interest in Adrien in the show, many fans tend to lean towards Chloé being attracted to girls, either partially or entirely, with her over-the-top interactions with Adrien being a result of her repressing or hiding her true orientation for whatever reason. Typically when these Chloés go through a redemption arc, they tend to drop their obsessive interest in Adrien and openly show their genuine interests.
- A number of fans have agreed that if Luka and Juleka were both brought into an akuma battle (either as their canon hero identities or something else), they would immediately figure out each other's secret identities, usually by way of one of them saying Something Only They Would Say in the vicinity of the other.
- The Kwami will react very seriously to any sort of Deal with the Devil being offered or performed in their vicinity, having very personal and deep-set hatred of any sort of demon (or similar crossover character, like Kyubey) that offers these for their misuse of humans. Especially Plagg, who will immediately drop any jokes or laziness and become dead serious and usually suggest instant use of Catacylsm on said being and insist on teaching Adrien the most effective ways of destroying them. The Kwami often tend to have a history with these beings, either as ancient enemies for all of time or having once trusted such beings and regret the decision centuries later when they discovered their true motivations and their ill effects on the humans the Kwami love. This is a fanon that makes sense for the characters in question to have, but the Quantumverse has yet to imply it has devils in it meaning it is yet to be confirmed (the closest beings to the above being a hint of the existence of genies, which are not given an implication of trying to screw over humans).
- A common idea, especially in older fanfics, is that the Miraculous can only work on humans. If someone was to lose their humanity, they would not be able to use a Miraculous at all. Over time this concept, while never disproven in canon (as no one has lost their literal humanity and tried to use a Miraculous), is shown to not be quite so cut and dry as first Robostus, a artificial intelligence in a robot body, was given no indication that he couldn't use the Miraculous by those who would know otherwise. More definitively, Season 4 would feature a Sentimonster replica of Nino use the Turtle Miraculous without issue and Season 5 would show a Sentimonster with undeniable free will, Félix, use the Peacock Miraculous, making it more likely that any sapient lifeform capable of speech can use a Miraculous versus the idea that only humans can use one.
- The idea that the Ladybug and Cat Miraculouses are always used in pairs, with pairs between them appearing throughout history. In canon, while Tikki and Plagg are clearly close, the only known meeting of the two users in canon prior to Ladybug and Cat Noir had the two on opposites sides of the Hundred Years War, making this fanon a shaky concept in canon.
- It is believed that Colt Fathom's abuse also extended to his wife, this is because Amelie (unlike Gabriel) never showed sadness over the death of her partner. And considering how protective she is of her son, it would make sense that she would try to stop the abuse, but failed to do so.
- Following the reveal that Lila is wearing a wig and has multiple fake identities, people have started believing the following:
- She is a grown woman who disguised herself as a teenager.
- She is Manon Chamack coming back from the future.
