Another possibility is that Loki teams up with other characters. He could form an alliance with the Avengers or some other powerful beings in the universe. Together, they could come up with a plan to stop Thanos. Loki could contribute his unique skills, like his ability to shapeshift and infiltrate Thanos' ranks, and then they could launch a coordinated attack.
Well, one possible plot could be that Thanos uses his mind - controlling powers on Loki to make him steal powerful artifacts for his collection. Loki, being under Thanos' control, has to go against his own nature at times. For example, he might have to target Asgardian relics that he would otherwise protect.
Well, in some fanfictions, Loki is often depicted as more powerful than Thanos because of his magical abilities. Loki is a master of illusion and deception. He can create complex illusions to mislead his opponents, including Thanos. Thanos, on the other hand, mainly relies on his brute strength and the Infinity Stones. But Loki's magic can sometimes outwit Thanos' straightforward power plays.
Power is a common theme. Both Thanos and Loki are power - hungry in their own ways. In fanfictions, they often either compete for power or try to use each other's power for their own goals. Another theme is redemption. Sometimes Loki is seen as a way for Thanos to find redemption, or vice versa.
There might be a moment where Loki discovers a crucial piece of information about Thanos. For example, he finds out the true source of Thanos' power and figures out how to cut it off. This discovery could be a turning point in the fanfiction.
Loki and Thanos are the central figures. However, characters from Loki's family such as Thor could also be significant. Thor might notice the changes in Loki and try to rescue him from Thanos' control. Additionally, characters like Heimdall, who has the ability to see across the realms, could be involved in detecting Loki's unusual behavior and Thanos' influence.