One common theme is envy. Loki may envy Thor's position, strength, and the love he receives from the people of Asgard. This envy can drive Loki to do things he might not otherwise do, like plot against Thor or try to prove himself in extreme ways.
One possible fanfiction could focus on Loki's struggle with always being in Thor's shadow. Since he is the little brother, he might feel overshadowed by Thor's popularity and heroic deeds. Loki could be trying to find his own identity and purpose, distinct from just being Thor's brother. This could lead to a story where he embarks on a solo adventure, facing challenges that force him to rely on his own wits and magic, rather than Thor's strength.
There's 'Thor's Redemption in Loki's Arms'. In this story, Thor realizes his true feelings for Loki after a series of events that nearly tear Asgard apart. It's a tale full of emotion and character development.
Well, one possible plot could be that Thor and Loki's little sister has some special powers that are a mix of their own. She might be caught in the middle of their feuds, trying to bring peace between them. For example, she could use her powers to stop Loki from his mischievous plans that would anger Thor, while also making Thor understand Loki's motives better.
Loki, on the other hand, might be in awe of Thor. He could look up to him as the ultimate hero. At the same time, he might also be a bit rebellious. Even as a baby, he could have that spark of mischief and try to break the rules Thor sets for his safety, which would lead to some comical or tense situations between them.
I really like 'A Different Path for Loki'. In this fanfiction, Loki is given a chance to redeem himself in a unique way. It's full of interesting plot twists and great dialogue between Thor and Loki. The author does a wonderful job of exploring Loki's psyche and his relationship with Thor against the backdrop of the Asgardian world.
When Thor is mean to Loki in fanfiction, it can lead to a downward spiral in their relationship. Loki, feeling constantly attacked, may lash out in more extreme ways. Thor, on the other hand, may double down on his meanness, believing it's the only way to deal with Loki. This can create a cycle of animosity where any love or brotherly bond they had is overshadowed by anger and distrust. For example, Loki could start to form alliances with Thor's enemies out of spite, and Thor would see this as confirmation of Loki's untrustworthiness, making the relationship even worse.
Thor might initially go into denial. He can't believe that Loki is truly gone. He may hold Loki's body for a long time, as if waiting for him to come back to life. Then, he could become angry. Angry at the situation, at whoever or whatever caused Loki's death. Eventually, he may find solace in the memories of Loki. Remembering the good times they had together and using those memories to move forward.
If Loki survived in Infinity War fanfiction, it could have led to a very different outcome. He might have used his trickery to deceive Thanos in some way. Maybe he could have pretended to be on Thanos' side while actually working against him. This would have added an extra layer of intrigue to the story as the other characters would have been unsure of his true motives.
It could be Malekith. He might see the sister as a way to get to Thor and Loki and gain power over Asgard. Since she's a new and potentially vulnerable target, he could try to use her in his dark schemes.