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.
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.
Mainly, it's Bucky Barnes and Tony Stark. Bucky is the caretaker here. He has his own history, including his time as the Winter Soldier. Tony, on the other hand, is the deaged character. He's known for his intelligence and wealth in his normal state, but now as a deaged person, he has new vulnerabilities. While other characters might show up in the fanfiction, these two are the core around which the story is built.
One common theme is redemption. Loki has often done wrong in the Marvel universe, and in these fanfictions, Tony taking care of him is a step towards Loki redeeming himself. It shows that with the right support, even a 'villain' can change.
One great 'Tony takes care of Loki' fanfiction is 'A New Bond' on FanFiction.net. It shows Tony finding Loki after a battle, injured and alone. Tony decides to take Loki in and nurse him back to health. It's a heartwarming story that really delves into their characters.
At first, it would be rocky. Loki is used to being a trickster and Tony is a bit of a control freak. But over time, they'd start to respect each other. Loki would see Tony's intelligence and resourcefulness, and Tony would see Loki's power and potential for good. Eventually, they'd become like family, looking out for each other.
Well, one interesting plot point could be Bucky's struggle to adapt to taking care of a deaged Tony. He might have to deal with Tony's child - like curiosity and energy while also protecting him from potential threats. Another could be Tony's reaction to his new situation, perhaps he tries to regain his former knowledge and skills in a cute and clumsy way. And also, the relationship development between Bucky and deaged Tony is always a great part, like how they grow to trust and rely on each other.
He could also develop a better understanding of the 'light side'. Taking care of Harry, who represents so much of what the 'light side' stands for, even in his deaged state, makes Draco question his own alignment with the 'dark side'. This internal struggle can lead to significant character growth.
Their relationship would be a slow - burn. Loki might play some pranks on Tony at the beginning, which would annoy him. However, when they get into a really tough situation, like being trapped in a dangerous dimension, they have to rely on each other. Loki could use his magic to keep them alive, while Tony uses his engineering skills to find a way out. This shared experience would bring them closer and make them realize that they can be good partners.
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.
It's popular because it creates an interesting dynamic. Snape has always had a complex relationship with Harry in the original series. When Harry is deaged, it gives Snape a chance to start anew and perhaps be a different kind of influence. It also allows for exploring Snape's more nurturing side which is a contrast to his usual cold persona.