Virus Among Us (Voltron: LD Fanfic)
Keith finds himself struggling with things said in the past when Lance says something to trigger unfavorable memories. This creates tension between him and Shiro. Tensions increase even more among all of the paladins when Keith becomes ill unexpectedly, tying into a secret regarding Keith and Shiro.
Disclaimer - I don't own Voltron: The Legendary Defender. This story ties into Aliens Among Us. The story works with the theories that Keith and Shiro are brothers, but also the Keith is an alien theory which is floating around, but with a few twists.