I recently built a Toa Inika Nuparu with some red pieces, and so naturally, I had to come up with a story for him.  The story is:

Toa Nuparu found a way to go into the past (he was the one who built the Boxor, so he must have been good at making things) and went back a while.  In his time traveling, he accidentally wound up in an extremely hot place, which melted parts of his armor, and made some melt into other shapes.  He stole the Kanohi Vahi (the great mask of time) and turned evil.

That’s about it!  Sorry, I have taken him apart already, so I can’t include a picture.