It's a Mad World
Okay this is a sneaky trick on my part. This is a one time bonus, to be completed before the game actually starts. For it to be a complete background it has to start back when the town was still there and all the characters lived there. Then it has to go over your travels in the mean time. How they have changed, how they got their powers, explanations of enemies, allies, etc.
If one is completed then you get a bonus 25 pts. Yes, since this is a one time deal this goes above and beyond the other 50 pts. So in theory your character could have a total of 575 pts. Assuming you do a backstory, take on addition duties, and have the maximum matching complications.