The meaning of headfanon gets usually mistaked for the meqning of headcanon.
A headfanon is a fact that fans consider canon basing it off their immaginations, but it will never be accutaly canon. A headfanon, for the fact that it is not canonical, can contain random aspects of how a character looks like/ identify as / is attracted to.
I headfanon chihiro fujisaki as transgender, black whit vitiligo, gay and nonbinary becouse i want to.