Whether Ladybug and Cat Noir are truly equal partners. Does Ladybug constantly winning battles singlehandedly and essentially becoming Master Fu's sole confidant make her too overpowered compared to Cat and thus make him unnecessary, or is their partnership perfectly fair the way it is now (since Ladybug is the only one who can purify akumas and fix the damages and thus Cat must protect her at all costs)? It doesn't help that those who think that the partnership is unbalanced can't agree whether or not Cat Noir should become privy to everything Ladybug knows thanks to his Base-Breaking Character status.
Related to the above, there's debates as to whether or not Adrien should be the main focus of the duo over Marinette. Supporters of the idea argue it would make more sense if he were the lead character since the show's biggest Myth Arc is connected to his family, yet he ended up barely involved in it; critics of the idea argue that he doesn't have enough personality to make for a good lead, and that he already has too much focus in the show thanks to Marinette's crush on him (with a number of her choices — and the subsequent plots — revolving around him somehow). Others Take a Third Option, saying that they don't necessarily want him to become the main focus of the show, but do wish he'd have more relevance when it comes to plots involving his family.
The events of "Chameleon" and whether or not Marinette, Adrien, and the students were justified in their reactions are still subject to heavy and volatile debate.
Debates over which characters deserve a Miraculous at this point have been running through the fandom since the series began. It doesn't help that, at the rate the show's been going at, every major character around Marinette and Adrien's age is gonna get a Miraculous, if only temporarily.
Should Marinette/Adrien still be the endgame pairing at this point? On the one hand, you have the fans who love their dynamic both in and out of costume and argue that they have good reasons for not revealing their identities to each other yet and that the slow-burn nature of the romance is what makes it so appealing; on the other, you have the detractors who argue that the romantic tension and near-reveals have long overstayed their welcome and that the various actions Marinette and Adrien have taken as a result have made the pairing too toxic to be viable.
Their respective actions towards each other in the name of the pairing have particularly triggered plenty of arguments in the fandom. Fans are sharply divided between those who see the actions taken on both side as cute examples of harmless teenage love, those who decry Marinette as an uncomfortable case of the Stalking Is Funny if It Is Female After Male double standard and Cat Noir as an Entitled Bastard to Ladybug's affections who refuses to take no for an answer, and those who believe that only one half of the pairing is toxic while the other is completely innocent in the matter.
Season 3 as a whole has been contentious amongst the fanbase, largely thanks to debates over the prominence of Base-Breaking Character Lila, the direction taken with Chloé's character arc, and various actions taken by both Marinette and Adrien as a result of the Love Square.
The Season 3 finale especially gets hit hard with this. Was it a solid conclusion to the season that provided an interesting twist to the show's formula going forward, or is it a hackneyed mess of ass pulls and OOC moments? No one fan can agree on this, let alone which parts of it were well-written (with the handling of the Love Square, Chloé's actions, and Master Fu getting Put on a Bus being especially contentious).
The "if your identity is revealed, you lose your Miraculous" rule. Is it an interesting way of adding tension to the plot, since it gives the heroes a reason to keep their identities secret, or is it just an Ass Pull used to keep the Love Square going and keep certain characters (especially the ever-controversial Chloé) off the team? It doesn't help that the show itself goes back and forth on it, with heroes that had their identities outed still being seen with their Miraculouses in later episodes.
The recasting of Nino and Max from Ben Diskin to Zeno Robinson is shown to be this. Some people really like Robinson's take and think he does a great job. Others criticize Robinson for sounding too jarring and barely to Diskin's take. The fact that for the voice actor change — the belief that Nino, who is from Reunion island, and Max who is black, should be voiced by a black actor— only adds more fire to the controversy.
The "Senti-Adrien" fan theory — the theory that Adrien is actually a creation of the Peacock Miraculous — has become incredibly contentious in the fanbase. Its supporters argue that it would make for more interesting storylines surrounding Adrien's relationship with his parents, especially if he were to find out about it, and it could easily tie in to how Emilie's coma was apparently caused by using the Peacock; its detractors argue that it would rob Adrien of any agency as a character (since sentimonsters are usually controlled by whoever is holding their amok, and he could essentially be erased from existence at any time) and that there's no way it could be done without a flood of Fridge Horror implications being opened up. The fact that season 5 confirmed that the theory was canon — alongside Félix also being revealed to be a sentimonster, and Kagami all but stated to be one — has only dumped gasoline on the fire.
Depending on who you ask, Rose's abnormally large eyes are either cute, creepy, or some fusion of the two.
The Agreste family-centric Myth Arc has become heavily contentious amongst fans. Supporters love it for being an interesting and compelling plot, giving them some fan-favorite episodes, and for giving nuance to various villainous characters (mainly Gabriel, Nathalie, and Félix); detractors hate it for focusing exclusively on the Agrestes and associates at the expense of more interesting characters, for giving various backstory reveals that don't make sense on closer scrutiny, and for making the villains Unintentionally Unsympathetic overall.
While the majority of fans were overjoyed that Zoé was revealed to be sapphic, a few feel that a season 5 unrequited crush is too little too late, given the ground broken by other animated shows in the years around the time the episode where this was revealed aired.
Season 5 managed to rival season 3 as the show's most divisive season. There's plenty of debates online as to how good or bad it really was, and even then no one fan can decide which specific parts are good or bad, be it Marinette and Adrien's Relationship Upgrade (is it a sweet conclusion to the love story between the two or a bad case of Strangled by the Red String?), the treatment of various characters (did Chloé deserve to get Put on a Bus to Hell or was it way too harsh even for her? Was Lila becoming the new Big Bad an interesting take on the character or something that makes zero sense whatsoever?), the sentimonster reveal (a well-done twist or an Ass Pull loaded with Fridge Horror?), or the season finale (a good conclusion that wraps up the Agreste family Myth Arc nicely, or an absolute mess of a plot that leaves Gabriel a Karma Houdini?).
The Season 5 finale in particular proved devisive between fans in regards to Adrien's absence during the final fight against Gabriel as well as the fact he didn't learn the truth about his father or that he's a senti from Marinette. Some fans are quite upset, if not outright infuriated, arguing Adrien has the right to know and calling Marinette's and Adrien's relationship "toxic" because she keeps so much important information from him. Others, meanwhile, decided to withhold their judgement until future seasons, or even the end of the show, pointing out every season finale so far has also been setup for the next season.
Which is better: the movie or the show? Fans who believe the former is better argue that the movie managed to iron out a lot of the flaws the series' plot had and made the Love Square more interesting and believable, while fans who believe the latter argue that the show managed to explore the characters better and how the changes made for the movie were ultimately detrimental to the story as a whole.
