I tried to make the joke a bit easier to get for non-Hetalians or those who just plain don't get it at first like Usagi in the third panel, but just in case: think on some basics of what Hetalia is about (you can Google a synopsis if you honestly don't know), and what line Usagi uses to end her fandom-conversion story in panel 2.

Also, the friends pictured here are both in a rather large group of cosplayers I've started running with lately - they and others in the group, with permission, may appear in future comics depending on what happens.

Hetalia (c) Himaruya Hidekaz.