One of the girls who does appear is a total yaoi fangirl - she openly enjoys seeing her husband being molested by other nations.
It gets better: Hetalia was serialized in a seinen magazine (Comic Birz). Yes, the series known for its almost entirely female fandom can be called a seinen. World Stars also has the distinction of running on Shonen Jump's sister site Shonen Jump+, though there's less of a gap in Periphery Demographic in most works relating to that magazine.
As an additional sidenote, said author was living in New York when he came up with the idea, which probably explains why it seems as though it's not quite expectedly Japanese.
Each of the countries' quirks is based on what the country is famous for.
Switzerland and Lichtenstein are depicted as brother and sister, with Switzerland being extremely protective of her. In Japanese, they are voiced by Romi Park and Rie Kugimiya, respectively, similar to the relationship between their characters in Fullmetal Alchemist (Park as Edward Elric and Kugimiya as Alphonse Elric)
There's also Truth in Television, in that the two countries do view each other as "siblings" (wir sind bruder).
Estonia's character design was based on Himaruya's own looks. Not the hair and eye colors, though.
He also jokingly has called the character "the best character in the series"
For America's Maru Kaite Chikyuu they used the "Awesome" and "Music" straight from Lady Gaga's "Just Dance".
In the ending song from the movie, you can also hear him yell Yes We Can! at one point.
He explicitly says "Yes we can" in "WDC World Dancing", one of his character songs, too.
Romano/South Italy's character song actually uses the rhythm and tone of Tarantella Napolitana. Which makes sense given that when compared side by side, they sound exactly the same.
Poland's Marukaite Chikyuu incorporates elements from the Polish National Anthem.
In addition, it seems that Frontier Works did their work; you can sync-up both Poland and Lithuania's Marukaite Chikyuu, and Switzerland and Liechtenstein's Marukaite Chikyuu, so they sound somewhat like duets. Furthermore, within the recent World Twinkle character CDs, each character references the other character with whom they share a CD with. This is most prominent on Norway and Iceland's CD, where they call/receive a call from one another midway through their songs.
The first edition versions of volumes four and five of the Japanese manga had special booklets.
The Japanese DVDs come with CDs containing audio dramas and character songs.
The first run of the DVDs in North America came with Hetalia-themed bandanas.
Cross-Dressing Voices: Averted and disproved for Iceland. A popular and old rumor was that he would be voiced by Mitsuki Saiga, while fans often assumed that a female would eventually voice him anyway. His voice actor for The Movie wound up being a relatively unknown male one, Ayumu Asakura.
Avoided for Hong Kong. Lots of fans speculated about which female seiyuu would play him, but both the CD drama and the Special Episode of the anime gave him a male one: Motoki Takagi.
No Export for You: While the team Hetascanlations has been making unofficial scanlations for years, and it's even gotten official releases in Germany, China and Thailand, the manga publications of World Stars have yet to see an English release.
Old Shame: Himaruya has deleted some strips and illustrations for the series over the years, probably for Unfortunate Implications and mistakes that he later corrected.
The Other Darrin: In the case of Romano's younger self, initially voiced by his older self's actor in the first episode, then switched in episode 60.
In World Twinkle, Taliesin Jaffe took over voicing England for a very good reason, as Scott Freeman was convicted for child pornography. Jaffe himself was replaced by Steven Kelly in World Stars, presumably due to being busy with Critical Role.
Shrug of God: About a lot of things ranging from how the nations are born, what exactly happens to the personifications where their nation no longer exists, to if/when certain nations will appear in the series.
Star-Making Role: Particularly in the dub, where it helped to kickstart or bolster several VAs' careers.
China and Taiwan are both voiced by Yuki Kaida in China's drama track and in the anime, as well as both being voiced by Clarine Harp in the dub.
And in Taiwan's character song, Kaida has a duet with herself as China makes a special appearance!
What Could Have Been: Many of the characters were originally quite different than how they were eventually portrayed.
Italy wasn't originally intended to have his Idiot Hair, but Himaruya drew it in at the last minute to make him appear cuter. His personality was also originally to be similar to a character from Himaruya's first series, Advance! Kitakou Broadcasting Club in being simply unlucky and cowardly, not being that much of a ditz.
Early notes in a booklet included with the special edition of volume 3 revealed that Germany was to be more of a "scary" character and moodier, but became more of a sympathetic type as the story evolved.
According to volume 3, China was going to be middle-aged and have short hair and glasses, and be more like Austria in personality.
According to volume 3, America was supposed to have been more handsome, more cheeky, and smarter. Himaruya has stated that the original version would not have worked out that well.
Himaruya originally considered giving England normal thin eyebrows, as well as making him an older man who attempted to dress trendy and younger. He changed his mind on the eyebrows after deciding he wanted them to mimic the brow patterns of a Shiba dog.
France was originally planned as a straight stereotype of a completely suave character, and he would have had visible wrinkles and shorter hair. Like America, he actually appeared in the strips with some of those physical characteristics before the Art Evolution hit.
According to volume 3, Russia was originally had dark hair, was middle-aged, and was going to be a crybaby whose personality changed completely when he got drunk.
Along with the idea for Hungary as a man, Himaruya had another idea for her personality, with her being a snide and witchy type of woman who would shoot people full of arrows if they mistook her for a guy. The basis of her current design and this rejected personality were in turn recycled from a Hungarian witch character in a series that never materialized.
Prussia was initially to have long hair and facial characteristics more like Poland, as well as being more mature.
At first Himaruya considered having Liechtenstein emulate her brother even more, with a harsher personality and a cold manner of speech.
According to volume 3, originally Greece had glasses and shorter hair.
Poland was initially intended to be the first female, while Hungary was to be male.
According to this blog entry, Belarus originally was supposed to be a brunette and quite more mellow and stable. A remnant of this idea can be seen in her first colored manga appearance, where her facial expression when threatening Latvia is a little less severe, while her hair and eyes are both colored brown.
Volume 3 notes also revealed that Himaruya played around with the idea of a Tsundere Belarus who was hot-tempered and constantly nagging.
Ukraine was to originally have a more average-sized chest, but in contrast, her personality would have been less dignified and she was to be even more unlucky.
Cuba was initially set to be a cute boy who was kinder, yet still strong-willed.
A prototype design for Korea had the character as a girl◊ with aspirations to be a pop idol. The design for the female Korea was inspired by the lead of an earlier, short-lived webcomic by Himaruya, entitled MoeKan (and even directly resembled her in one of the drafts). It was also re-used for his canon Gender Flip self.
He was also supposed to be in the anime, but then the South Korean government, Moral Guardians declared a Dude, Not Funny! on the character note While both Kids' Station and Studio Deen denied there ever was to be a Korea character in the anime, he did appear in the first ending sequence and in a character design on the website (that was removed shortly after the controversy), as well as an animation error in episode 14 (when they removed his role from the plot, but forgot to do a retake on one scene that showed him from behind). Fans can still dream though since Himaruya did not dispose of him, at least in his blog, as of 2010-11.
Nagasaki originally had ribbons in her hair and looked more like Seychelles (who in fact was based from that old design).
Okinawa was originally to be a girl with flowers in her hair, as shown in a discarded sketch in one of Himaruya's galleries. She was also an Expy of Tira Sugusuku, a character existing in both the Barjona and Kitakou series. However, a girl resembling the original design (or Tira) can be seen at his house in his debut.
In the dub, Todd Haberkorn was originally cast as Britain, but the role of Italy ended up having to be recast.
Apparently, the recasting of Italy ended up delaying the dub for a while because they couldn't decide between Todd Haberkorn and Vic Mignogna.
Also with regards to the dub, Montgomery Sutton may have voiced Denmark throughout season five at the least; however, production delays meant recasting Denmark, with Greg Ayres taking the helm from seasons five on.