Poland/Hungary

Poland/Hungary is a semi-popular and heterosexual pairing in the Hetalia fandom. They have never appeared together in canon, but are shipped together due to their histories. Poland and Hungary have had close relations since the middle ages;  this friendship is not only described by a bilingual proverb ("Pole, Hungarian, two good friends"), it also has its own holiday celebrated in both countries.

The fact that Hungary is a tomboy who seems to like effeminate males while Poland seems to have a tendency (at least in the early strips) to cross-dress, something fans cite to justify the relationship, is not a coincidence. Himaruya's original concept for Hungary was a cross-dressing male, while Poland was a female. When he created a female Hungary, he used that idea for Poland instead.