A word used in fandoms "headcanon"-is there a word in Japanese for it?

Question

I talk with a couple of Japanese users on social media and I was wondering what other words can I use to say "Oh, I have this theory", or "I imagine this and that about those characters". Up until now I mostly used the verb 想像する to say that I 'imagine" the following or saying イデア. While talking with an user they wrote this 妄想 and I was glad to know another word and I think it fits more, I believe with the term 'headcanon'. I'm gonna use the word more often, but if anyone knows other terms, please tell me! I hope at least it was informative for some, because it was the first time that I encountered the use of 妄想.

Answer 1

The most comon terms would be 「脳内設定{のうないせってい}」 or 「マイ設定」.

「妄想{もうそう}」("delusion") is an old, "regular" word; It does not have the slangy feeling or vives that the two "special" terms above or the English "headcanon" have.

You could use 「妄想」 in explaining what a headcanon is, but it could not replace the term all by itself. The word is just too broad and 「想像{そうぞう}」("imagination") is even broader.