I was just thinking since there's so much langst fanart and fanfic and just- The Voltron fandom really likes putting that boy through so much.
What about a curse of immortality au? Sorta like Kenny from South Park. You can even but a klance twist on it and say Keith is the only one who notices/can see the scars from past deaths.
Or Hunk, and have a brotherly-based fic. There is not NEARLY enough of those. Hunk is such an underrated character. Especially if you involve Keith in the mix still because they're pretty close friends.
An extra sad thing would be if Allura or Coran are the unintentional cause of the curse somehow. I would BAWL if I found a fanfic that had Coran unintentionally harming his unoffical space nephew, Jesus Christ.