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.
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.
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.
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.
Iruka and Naruto are the central characters. However, depending on the plot of the fanfiction, characters like the Third Hokage could be involved. He might be the one who gives Iruka certain instructions or permissions regarding Naruto. And then there are Naruto's friends from the academy, such as Kiba and Shino. They could be part of the story, for instance, joining Naruto in some training sessions arranged by Iruka.
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.
Obviously, Tony and Peter are the main characters. Tony Stark, also known as Iron Man, is a brilliant inventor and one of the founding members of the Avengers. Peter Parker, on the other hand, is Spider - Man, a young and enthusiastic superhero. Their interaction forms the core of this fanfiction.
Pepper Potts could be great. Even if Tony is deaged, she could still be his caretaker or friend in a different way. She could see his potential and help him navigate the world as a deaged version of himself. Another good character would be Rhodey. He could be like an older brother figure, protecting Tony and also being amazed at his young - but - still - brilliant self.
Well, clearly Harry is one of the main characters as he is the one taking care of the baby cousin. The baby cousin is also a main character, even if it's a young and not fully developed character yet.
A possible plot could be that Draco has to figure out how to reverse the de - aging spell on Harry. In the process, he might have to seek help from unexpected sources, like some old family magic or even some of the more reclusive wizards in the wizarding world. This journey could bring him and Harry closer together as they face various challenges and obstacles.
Chiron, the centaur who trains demigods at Camp Half - Blood, could also play a role. He might offer advice to Percy before he embarks on his journey with Poseidon or be there to welcome him back and help him adjust to life at camp again after his time with his father. His wisdom and experience can be a great addition to the story, especially in terms of Percy's growth as a demigod.