There could be. Fanfiction writers often take existing characters and put them in all sorts of situations. Loki, being a complex and popular character, and the Chitauri being a menacing force in the Marvel universe, might be the subjects of such a story. But it may not be easy to find, as it depends on the specific fanfiction platforms and how they categorize and tag their works.
The plot could start with Loki being stranded on a planet occupied by the Chitauri. They recognize him as the one who once led them but now see him as a weakened figure. So, they begin to use him for their cruel experiments. They could be trying to extract his Frost Giant powers or something similar. As the story progresses, Loki has to find a way to escape while dealing with the continuous abuse from the Chitauri, and maybe he even forms an unexpected alliance with some of his captors in order to survive.
It could also mean that there are fanfictions where Loki is depicted in situations that involve some form of abuse, which might be disturbing to some fans. However, in the world of fanfiction, different interpretations exist. Some might see it as exploring darker aspects of the character, while others may consider it going against the general perception of Loki. In many cases, such fanfictions might also violate the community guidelines of certain platforms if they are too extreme or violate ethical standards.
No, it's not that common. Fanfiction often focuses on more positive aspects of Loki, like his powers, his charm, and his interactions with Thor and other Avengers. However, 'loki is abused fanfiction' does exist for those who want to explore the darker, more complex sides of his character, but it doesn't have the same widespread popularity as other types.
Yes, there might be some out there in the vast realm of fanfiction. However, such a concept is quite dark and goes against the more positive aspects of their relationship in the original lore. Fanfiction often explores different and sometimes extreme interpretations of characters.
Platforms hosting fanfiction could enforce stricter content guidelines. For example, they could clearly define what constitutes 'abuse' of a character like Loki and not allow such works to be published. This would help maintain a certain standard in the fanfiction community.
Loki's character could develop in terms of his understanding of power. Through the abuse, he realizes that power can be misused like Odin does. So he may strive to use his own power in a more just way. He might also start to question the Asgardian way of ruling which is based on Odin's actions.
One possible storyline could be Loki's struggle to break free from Odin's abuse and find his true self. He might start to gather allies secretly, like some of the more sympathetic Asgardians. Another could be Loki's internal journey of dealing with the emotional trauma, perhaps having flashbacks of the abuse while trying to perform his duties in Asgard.
Loki would probably be defiant at first. He has a strong sense of self - pride and would not easily submit to Thanos's abuse. He might hurl insults and threats at Thanos, even though he is in a vulnerable position.
One possible plot could be that Thanos sees Loki as a tool that has failed him. So, he subjects Loki to various forms of physical and mental abuse to break his spirit. Loki, being a survivor, tries to find ways to outwit Thanos even in his weakened state.