- Sesshomaru is the Lord of the West, and he has a manor, home, or castle somewhere with servants and subjects. In the actual series he's a nomad with no home ever shown, he's not the ruler of any land anyway, only becomes a daiyoukai at the end of the story, and his only servants are the ones you see with him all the time - and those mostly seem to have latched onto him in spite of his preference. (This seems to have originated with sketchy fan translations, but the notion remains entrenched in the fandom.) This is sometimes expanded into a full demon hierarchy with numerous daiyoukai ruling other areas of Japan. Koga is a popular candidate.
- In fact, even Sesshomaru's father never bore any such designation, either. He is only ever called "Inu no Taishou", and while this would translate as "Dog General", in spirit the title could be much more broadly interpreted, which the English version wisely represented with the more ambiguous "Great Dog Demon". He is never explicitly stated as having "ruled" the West, only to have resided there.
- If fanfiction ever deals with Kagome growing older, she'll likely become some sort of doctor due to her experience patching up her friends. In The Final Act she is seen learning herbalism from Kaede so she'll likely become the village healer.
- Inuyasha's addiction to ramen. In the manga, he's seen eating it two times, and mentioning it tastes good. The anime shows his liking of it a little more but nothing remotely close to the Ill do anything for ramen you see in fanfiction.
- Inuyasha's tranformation to full youkai being triggered by anger. In canon its triggered by fear of dying, not anger; the Unstoppable Rage comes afterwards.
- In the absence of any Canon Names for them, it's common to see Inuyasha and Sesshumaru's father referred to in the English-speaking fandom as "Inutaisho" (a corruption or mishearing of "Inu no Taisho" which is then used as a name instead of a title), and Sesshomaru's mother is popularly called "Inu Kimi" (sometimes "Inu Kami"; the former, though more common, is probably a misspelling of the latter, which is Gratuitous Japanese for "Dog God").
- Hand in hand with the very common plot of "the youkai of the feudal era survive to the modern day" is the idea that charms and spells to mask youkai and youki are mass produced, usually as rings or necklaces. In the actual series, no such spells exist. In fact, it's heavily implied, if not outright stated, that only the most powerful of youkai can take on humanoid forms in the first place.
- Many fans assume that Jinenji is a horse hanyou because his face looks elongated and horse-like. But actually this assumption in the Canon is neither confirmed nor rejected.
Fanon / InuYasha