Prussia/Austria

Prussia/Austria is a common pairing in Hetalia: Axis Powers, involving the characters of Austria and Prussia. The pairing is sometimes referred to as the Water and Oil Pair, based on how water and oil don't mix, much like how these two characters cannot get along. A more common name for the pairing is PruAus, a combination of the first three letters of both of their country names.

Wars
During the War of the Austrian Succession (in which Austria says the infamous line about his vital regions being seized), Prussia was determined to claim Silesia for himself after the Maria Theresa was crowned the Archdutchess of Austria and Queen of Hungary.

Another war between them included the Seven Years' War, which ended in Prussia's victory.

Modern Life
Prussia takes pleasure in annoying and humiliating Austria in whatever ways he can, mostly bothering him when he's playing the piano or appearing uninvited (as seen in Episode 24, when he pops out of a bush to make fun of Austria on how cheap he is). Prussia always comments on how Austria is 'too uptight' or 'needs to loosen up', while Austria thinks Prussia is childish and irresponsible.

Prussia once proclaimed on his blog that he and Austria were staying at Germany's house. Austria also gets annoyed because Prussia dumps onto him unwanted items and items he was conned into buying (for example, a panda that was supposed to bring 'happiness' sold to Prussia by Hong Kong). Prussia also has a habit of stalking Austria.

In the Christmas webcomic Prussia and France try to strip Austria, as Prussia demanded that stripping and humiliating Austria will be his Christmas present.

In the Ore Sama no Drama CD, Prussia blogs that he went over to Prussia's house. Prussia annoys Austria by pinching his cheeks while exclaiming how squishy they are, while Austria tells him to stop. Prussia ignores him and takes a picture of them together. Then, he gets hit with a frying pan by Hungary, although he doesn't know this, and passes out. Austria shouts Prussia's name desperately several times after. Also, when the nations had thought Prussia was dead due to him eating England's cooking, they started grieving for him on his blog. Austria commented, calling him an idiot and telling him to "please come back alive". These events show that Austria genuinely cares for Prussia.

Fan Speculations
Some fans believe that Prussia's taunting and teasing is a way of hiding his true feelings about Austria, as he also mocks his brother, Germany who he clearly cares about. He is also seen crying whenever he sees Austria and Hungary together, but it is more likely that Prussia holds affection for Austria rather than Hungary, as he stalks Austria, not Hungary.

Others think that since Austria talks about hating Prussia so much, or just talks about him in general, he secretly holds affection for him, despite his stubborn attitude. It's commonly portrayed as the actions of a tsundere.

Webcomic: Extra Stories

 * Maria Theresa and the War of the Austrian Succession
 * Maria Theresa and the Seven Years' War
 * Summary of the Austrian Succession
 * Christmas 2007 Summary (Part 6)
 * Liechtenstein's Journal of Swiss Dopiness