A typical plotline in Loki deaged fanfiction is Loki being deaged due to some magical mishap. This then leads to him being in a situation where he has to rely on others, which is a big change for him. For instance, he might have to rely on the Avengers (if it's set in that universe) for help. Another aspect could be that deaged Loki has to face his insecurities from his childhood all over again. This can be really interesting as it shows a different side of Loki, a more vulnerable side that we don't often see in the original stories. There are also fanfictions where deaged Loki tries to regain his old age as quickly as possible while still causing some trouble along the way.
One character that would be really interesting to pair with deaged Loki is Doctor Strange. Strange could be the one to help Loki figure out how to reverse the deaging process or use his new situation to his advantage. Also, if we consider the Avengers, Natasha Romanoff could be paired with deaged Loki. She could teach him some skills that he might not have learned in his original upbringing, like stealth and espionage. And Steve Rogers could also be a good match. Rogers' sense of honor and justice could have an impact on deaged Loki and maybe even inspire him to be a better person.
A great plotline might involve the deaged characters interacting with their younger selves' memories. Weiss could be haunted by her family's expectations in a new light, as if seeing them for the first time all over again. This could lead to her making different choices and growing in a whole new direction.
One popular plotline could be Loki being the new student in high school where the Avengers are also students. Loki might initially try to cause trouble, like pranking the other students or trying to steal something important for a school event. Another plotline could involve a school competition where the Avengers and Loki are on opposing teams, and they have to learn to work together in the end. And there could also be a plot where Loki has a secret crush on one of the Avengers and tries to hide it while still being his mischievous self.
The plot might involve Tony taking on a paternal role towards deaged Loki. He could start by providing basic care like food and shelter. As time passes, he discovers that Loki has a fear of being alone in this new state. Tony then tries to help Loki regain his confidence. They might also face external threats as some villains might try to take advantage of the deaged and vulnerable Loki. So, Tony has to protect Loki while also trying to reverse the deaging process.
A unique plotline could be Percy being deaged and having to hide his identity from the new demigods at Camp Half - Blood. He has to pretend he's a new camper while secretly trying to find a way to reverse the deaging.
One interesting plotline could be Harry and Draco being deaged and having to rely on each other in a world that seems new to them again. They might form an unexpected friendship as they don't have the pre - conceived notions from their older selves. For example, they could team up to solve a mystery in Hogwarts that only they, with their combined knowledge from before, can figure out.
One possible plotline could be Anakin having to re - learn the ways of the Force as a child while also dealing with his past memories. Another might be how the other Jedi react to this de - aged Anakin, whether with suspicion or a sense of protectiveness.
One plotline could be that the de - aged Voldemort, now in a more innocent state, tries to make amends for his past actions towards Harry. He might use his knowledge of magic to protect Harry from other threats in the wizarding world. Another could be that Harry initially resists the idea of Voldemort as a father - figure but slowly comes to understand that this new Voldemort is different. And then there's the plotline where the wizarding world is in chaos because of this strange relationship, with some people believing it's a dark plot while others see it as a chance for redemption.
One interesting plotline could be Severus having to take care of a deaged Harry. He might struggle with his initial dislike for Harry but gradually grow to understand him better in this new situation. For example, he could teach the young Harry some basic potions skills, which would be a unique bonding experience.
Initially, Tony's relationship with deaged Loki is one of pure obligation. He has to keep Loki safe and figure out how to get him back to normal. However, as he takes care of Loki, he discovers that Loki has a curious and intelligent side even in his deaged form. Loki, for his part, is used to being alone but starts to enjoy Tony's company. They might have some arguments along the way as Loki still has his stubborn streak. But through shared experiences, like facing a common enemy together or just spending time exploring Earth, their relationship evolves into a deep and trusting one.