Uncanny Valley/Fan Works

In With Strings Attached, Brox looks and acts like a normal little child—until he/she starts acting his/her real age. Her/his whole mien shifts, which creeps out the four considerably.
Nebiros in New Dawn is already an outlandish looking demonic clown, barely even human looking, so it might count as an aversion, as he does not look human enough to qualify for the trope. However, it is played straight with his speaking patterns. He talks as a whole like a young teenager, has no sense of personal space, views reality as a game and is oh so enthusiastic in a very child-like way about what he does. And, suffice to say, he does not see anything wrong with being a serial killer: "Because its so fun, watching em flail about like a fishy!"
In X-Men fanfic Mutatis Mutandis, Northstar is basically described as vampirically beautiful. Rogue notices when she stares at Northstar's face for more than a few minutes, he looks so eerily perfect that he seems creepy and surreal.
Kimi no Na Iowa:
- Most Summoned/Manifested shipgirls are inhumanly mechanical and precise in their motions, to the discomfort of observant humans. Also inverted in that they find Natural Borns too human.
- In Chapter Eight, the more humanlike abyssals are called simulations that still wouldn't fool the sober.
- In Chapter 12, Shimakaze tells Ayaka of how she finds fourth-plus generation Japanese diaspora off.