[Asami]

Headcanon it means something you think of that you wish happened in the series.
Or this Used to describe something that hasn't yet happened in original canon but has happened in their head.

Here's my super sad headcanon for harrypotter

Harry potter headcannon- after the battle of hogwarts was over and all the dead were buried, one man stood over the grave of Colin Creevey. He leaned over and placed something next to the headstone and left. He had placed a picture of a smiling boy with unruley black hair and a scar on his forehead that was signed "to Colin.. my biggest fan - Harry Potter"