Fan Casting Like Brother and Sister in Fictional Character Pairings

Sometimes, two characters of the opposite are very close — so close that you might expect them to be dating. Except they're not. They admit that they matter a great deal to each other, that they would die for each other, that they can't imagine life without each other. They aren't just any pair of friends. They're as close as family. They're like brother and sister! Often, other people don't believe this. They assume that the couple must be dating — or at least that they secretly wish they were. When the couple say they are like brother and sister, they will point out the one tiny but debilitating flaw with their theory: they are not brother and sister.