Hetalia: Bloody World

In a Post-apocalyptic world, its survival of the fittest and when someone dies or goes missing it's no questions asked. Unless it's your lover/brother, then it's kill everyone who's involved until you find your brother which is precisely what Alfred's in the midst of doing. UsCan, RusPrus, Frain, Iggychu, and a bit of UsUk. Other couples show up too.