Alternative Character Interpretation: Axis Powers Hetalia
Since the cast of Axis Powers Hetalia are nations and the series itself is mostly light comedy, this is to be expected. A few strips hint at much darker humor or hidden angst; fandom often takes the idea of history-as-canon and carries it to the logical conclusion. This makes for potentially VERY dark characterizations for most countries, especially those with imperialist or colonialist eras.
There's also a surprising amount of fics in which Italy is not as innocent as people like to think and that he lied about being a virgin to Germany. Saying that he is like his Grandpa in that he has a way with women and that he can be a real tease if he wants to be.
A lot of fan authors and fanartists depict a very close, loving, brotherly relationship between Canada and America, even though the manga describes America as "the root of Canada's unhappiness" and it's shown that Canada, while not outright hating him, resents his brother a lot. So much that his Crowning Moment Of Awesome consists of almost talking America to death. On the other hand, some fans posit that all this is just typical sibling behavior and that just because Canada likes cutting America down to size occasionally, it doesn't mean that he doesn't genuinely love and care for his brother when the chips are down (as evidenced by him consulting America for advice at least once in canon).
This makes sense since in Real Life, Canada and the United States are currently the world's largest trading partners, share the world's longest border, and have significant interoperability within the defence sphere (NORAD, for example, covers both countries). While Canadians will always make fun of the US and vice versa, it's also well-known that each would be sunk without the other.
And then there's his (admittedly complex) relationship with Japan. Is China's obvious affection for Japan purely familial or more than that, and in either case, does Japan simply not return China's affections or does he actually reciprocate them (familial or otherwise) and is just reluctant to admit it? And while we're on the subject of relationships, just what does China think of Russia, especially after the Cold War/Sino-Soviet split?
Also, we cannot forget his relationship with Hong Kong and Taiwan. A well-meaning Team Mom who nags his younger siblings and inadvertently pushes them away while trying to help them, or a dangerous Yandere who would rape them into submission if he could?
Taiwan and Hong Kong themselves are subjected to this too. Is HK a real Emotionless Boy whose psychological development was stunted while growing up with England, a Sugar and Ice Personality who cares deeply for China and the others and just Cannot Spit It Out due to his mixed raising, or just a Comically Seriousprankster who deals with said baggage by playing tricks on everyone and just doing what he wants now that he can do it? Taiwan: was she married/engaged to Japan in the past (more exactly, during the time she was his colony), is her liking of Japan mostly based on rebelliousness towards China than real feelings for him, is she a victim of Stockholm Syndrome after her times with Japan, or is she Yanderetowards him - like Belarus is towards Russia (only more subtly)?
There's the recent trend of making Spain a Yandere or Cute and Psycho, due to extremely complex real world history. In the character descriptions in the books, it's mentioned that Spain is "scary when angry", and that he's "dangerous when drunk". It's not clear if the latter means he's dangerous in the France way or the aforementioned Yandere way, but these notes are good enough for the fanartists and authors to build up on. There used to be notes on the site indicating that Spain's treatment of Romano was in direct contrast to the rest of his colonies.
Most fanartists depict Japan's personality by the clothes he wears - if he wears his usual white uniform as shown in canon, he is (mostly) normal, but if he wears a black uniform, he is one of the above. Sometimes, the two are warring with each other.
If they're not fighting each other, they're having sex. There's no way around it.
About his rival Turkey: Jerk with a Heart of Gold who has a soft spot for Japan and actually cares for Greece deep down? Loveable Sex Maniac who hits on anyone he thinks would make a good harem member? Jerk Ass who gets his kicks out of provoking any kind of reaction from his longtime rival/BST partner? Manipulative Bastard who'd rape Greece just to put him in his place and make him kowtow to him? And did he rape Hungary or not right before/after the fight that was followed by her and Prussia more or less realizing her real gender?
Italy Romano: A misunderstood grouch with simply a huge inferiority complex stemming from his grandfather ignoring him and feeling that Spain and others want to use him for his inheritance, a useless whiny manchild who was too spoiled of a brat that still deserves to be spanked, or a grade-A Jerk Ass that simply likes being an annoyance to everyone? Then there's the matter of if he has "deeper" feelings for Spain but acts like a jerk to throw him off, or if he actually hates Spain and is just stringing him along in hopes to manipulate him as payback.
Let's add Korea to the list of APH characters who get Darker and Edgier characterizations in Dark Fic, shall we? It's especially noticeable with him as his normal characterization is as an unfailingly cheerful if somewhatoverbearing guy with a hilariously overzealous affection for China, and the typical "serious" characterization of him essentially filters these qualities through a dark looking glass, reinterpreting his intense devotion to China as a hint to how his cheerful and childlike demeanor conceals an emotionally disturbedor stunted individual. There's even a semi-popular fanon theory that Korea actually represents both Koreas and suffers from multiple personality disorder with "North Korea" arising from his bottled-up negative emotions, even though it's been confirmed that South Korea and North Korea are separate characters.
Then there's Poland. Ditzy airhead with an affinity for wearing skirts and playing with pink ponies? Or a Phoenix-like character who always stands his ground and refuses to give up no matter who tries to beat him down? Or both? There's no rule that says he can't be a PluckyDeterminator who just happens to really like wearing skirts and playing with pink ponies, after all.
There's also Sweden. Is he totally as the comics seem to (and fandom loves to) portray him as? A misunderstood and much kinder on the inside guy than what his thug-like face says? On the other hand, if he exudes such a constantly threatening aura that's likely worse than even Russia's, where does that come from? Was he really a doting 'husband' to Finland or was he controlling and possessive? He does get rather grouchy at the implication that Finland might have been happier with Russia. Is he uncomfortable with how scary he looks, or does he willingly intimidate others? And who let this terrifying man buy a child off the internet, anyway?
Is Finland still "living" with Sweden because he genuinely cares for him? Is he next to Su-san's side just because of Stockholm Syndrome? Or hell, can it beboth in the end? Sweden himself seems to be quite enamoured with Finland, but Finland's side of the story is not that clear if you think about it.
Some people have characterised him as being almost at ADHD levels or having the mind of a young child, even though he seems rather tame in his canon appearances, with a few strange moments (wanna history lesson on Vlad the Impaler, anyone?).
Belgium can vary widely in fanfics, most often being portrayed as either The Ojou who is rather girly in her dress and attitude, affectionate towards her older brother, Spain, and Romano, and is relatively easy-going, sometimes to the point of being an Extreme Doormat, or The Lad-etteAction Girl who often is The Tease towards the men around her.