A fanfiction could explore Loki having dark circles as a result of a curse. He has to find a way to break it before it completely drains his power. Along the way, he meets a group of Midgardians who mistake his dark circles for some kind of new fashion trend. Loki initially finds this annoying but then uses it to his advantage to blend in while he searches for a cure.
One idea could be a fanfiction where Loki uses his magic to cover up his own dark circles. Maybe he's been up all night plotting against Thor and is trying to look his best in front of the other Asgardians. He could accidentally create a spell that gives everyone in the palace dark circles instead.
A plot twist could be that Loki's dark circles are actually a sign of a hidden power. In the fanfiction, as Loki discovers this, he has to learn to control this new aspect of himself. It could be that the darker the circles, the more powerful he becomes, but he also risks losing his sanity if he doesn't master it.
One idea could be Loki having to team up with an unexpected ally from Asgard's underworld to stop a new threat that emerged during the events of 'The Dark World'.
Another plot could be a what - if scenario. What if Loki didn't fall into the abyss in The Dark World? He could have used his trickery to manipulate the dark elves in a different way. He might pretend to side with them at first to gain their trust and then double - cross them to save Thor and Asgard. This would show his complex nature and his loyalty to his home, in his own twisted way.
One main cause is lack of sleep. When you don't get enough rest, your blood vessels under the eyes can become more visible, creating the appearance of dark circles. Another factor could be genetics. Some people are just more prone to having darker pigmentation around their eyes. Also, allergies can play a role. Constant rubbing of itchy eyes due to allergies can lead to inflammation and dark circles.
You can try getting more sleep. Adequate sleep helps your body to recover and can reduce the appearance of dark circles. Using cold compresses can also be effective. Just put a cold, damp cloth on your eyes for a few minutes. It can constrict blood vessels and lessen the darkness.
Maybe Loki pretends to be a mortal female to infiltrate a powerful wizard's lair. He has heard that the wizard has a weakness for mortal women. As a female, Loki is able to charm his way into the lair. Once inside, he discovers that the wizard is planning to use a powerful spell to take over all of Asgard. Loki then has to figure out a way to stop the wizard while still maintaining his female disguise.
One idea could be a story where Loki teams up with the Winchester sister to battle a common supernatural foe. Maybe they start off distrusting each other, but as they face challenges, they learn to work together. Loki's trickery could be both an asset and a source of conflict in their partnership.
One idea could be that Loki, being the mischievous character he is, finds his way into the wizarding world of Harry Potter. He could start causing chaos in Hogwarts, perhaps by disguising himself as a student or a professor and playing pranks that are far more elaborate than those of the Weasley twins. For example, he might turn the entire Great Hall into an ice rink during breakfast time.
One idea could be that Loki gets turned into a vampire while in the midst of his schemes against the Avengers. This new state gives him different powers and motives. He might struggle with his newfound thirst and also use his vampire abilities to outwit the Avengers in different ways.
Dark Loki Fanfiction can be appealing because it often delves deeper into the psychological aspects of Loki. We get to see his inner turmoil, his possible descent into darker paths. It can also create more intense and complex relationships with other characters. For instance, his interactions with Thor or other Asgardians might be completely different in a 'dark' scenario, which makes for a very interesting read.