Calais Reed
It's really hard to write a backstory for a Homunculous...
:/ Well, they're all born from Father, so you could say something about what Father told said homunculus to do.. or who said homonumculus was an embodiment of (Wrath, Pride etc.)
And then detail your experiences in the country. It doesn't have to be really long, and if your homunculus is the type who sees himself/herself above other people, you could put how agonizing your experiences with people were or something like that. It's all up to you.