A Certain Scientific Prussian (Hetalia/To Aru Kagaku no Accelerator)

Takes place before the events of the manga series.

Japan announced that their next World Meeting at his place will be in none other than Academy City. Upon arriving at the city, Prussia started acting....strange. Meanwhile, a secret rogue organization has received information about the existence of these country personifications and are out to get them. So far, the countries had heard and seen a lot of unexpected things in Academy City, but they were definitely not prepared for Prussia's big secret.

I do not own anything in the story except the plot.