http://www.fanfiction.net/read.php?storyid=638415
This is a Tenchi Muyo fic.
A dark what if, this centers on the idea that Kagato took a final precautionary measure against a member of the Masaki house.
*Last spoiler warning, this story should really be read without any knowledge of the plot*
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Okay. Kagato encoded a degenerative disease into Ryoko, which activates a bit after Kagato's death. The rest of the story revolves around how the rest of the cast deals with Ryoko's slow decline into a painful death. 
Overall, I like this story, albeit with a few nitpicks. I had problems buying that Washu could not manage to cure Ryoko in the time given. A contrivence, perhaps, but one that I could live with. My only other gripe is the Akeya/Tenchi romantic angle.  While I'm not opposed to any particular Tenchi matchups, I don't think he went about this one in the right way.  It felt...morbid, more than anything else.  Maybe this helps the story for some, but I didn't care for it.