Board Thread:Off Topic/@comment-25396609-20160319212213/@comment-25396609-20160320041804

The problem comes with inserting them into the story, as that is the point it slides into mary sue territory.

having them know eachother is fine, but if it is significant enough to go into the character sheet (which is basically an outline of the character as a whole, or a snapshot of them at a particular moment in time) then you are likely going to have a problem.

It's a tricky balance if you want them affiliated with the main characters, and extremely difficult to avoid having go horribly wrong.

I personally prefer to place an invisible wall between my characters and the canon, with the most direct interaction being in, say, a sparring class or similar.