He might develop new combat skills. Loki's familia members could teach him different fighting styles or strategies. For example, he could learn from Finn how to better lead in a group combat situation, which would be a significant change from his more solo - focused adventures before.
In this fanfiction, Bell might be recruited by Loki for a special mission. Since Bell has shown great potential in combat and dungeon - delving, Loki could see him as an asset. Bell would then have to learn to work with Loki's familia members, like Ais, in a new context, which could lead to some interesting character interactions and growth for Bell.
One possible character development for Loki is that he becomes more empathetic. Hulk's simple and straightforward emotions could rub off on Loki. He might start to feel genuine remorse for his past misdeeds. On Hulk's part, he could become more diplomatic. Working with Loki, who is a master of manipulation and politics in a way, Hulk could learn to use words as well as his fists to solve problems in the fanfiction.
Ash might start to become more devious. He could learn some of Team Rocket's underhanded tactics, which would be a big change from his usually straightforward and honest self. But at the same time, he could also be a force for change within Team Rocket, slowly making them less evil.
Well, for Loki, his development could be about finding a new purpose. Instead of just causing chaos, he has someone to care for. He might become more selfless. The baby Frost Giant, on the other hand, could start to show signs of leadership as it grows. It could learn from Loki's cunning and use it for positive things in the future, like uniting the Frost Giants in a more harmonious way.
One possible plot development is that they team up to take on a common enemy that neither of their villages could handle alone. This enemy could be a powerful rogue ninja or a group with a dangerous new jutsu.
Perhaps Percy joins a special unit in the military. In this unit, he discovers some sort of conspiracy or mystery within the military structure. This could lead him on a journey to uncover the truth while still fulfilling his military duties. He might also face some moral dilemmas along the way as he tries to do what's right for the military as a whole.
One aspect that can be explored in Freya and Bell fanfiction is the idea of destiny. Freya believes Bell is destined for great things, and she wants to be a part of that journey. A fanfiction could show how she subtly influences Bell's choices in the dungeon, leading to both growth and conflict. Bell might start to question why certain opportunities seem to present themselves so conveniently, and as he discovers Freya's role, he has to decide whether to accept her help or forge his own path.
Naruto could develop a more brooding personality. With Uchiha blood, he might be more in touch with his emotions, like the typical Uchiha. He'd also be more interested in the Uchiha clan's history and techniques. His power growth would likely be faster as he'd have access to the Sharingan, which can quickly boost one's combat abilities.
Well, it could be that her joining Voldemort causes a huge shift in the balance of power. The wizarding community would be in chaos as they try to figure out how to deal with this new threat. Dark Fem Harry might also start to influence Voldemort in unexpected ways. Maybe she convinces him to use more psychological warfare rather than just brute force. And she could be the one to find and destroy some of the remaining Horcruxes of other wizards, believing that it would make Voldemort even more powerful and thus her position more secure.
One possible development is that Naruto would have a different sense of identity. In Kumo, he wouldn't be the 'container of the Nine - Tails' in the same way as in Konoha. Kumo might have different plans for him regarding the Nine - Tails' power. This could lead to him either suppressing the power more or using it in a more aggressive way. His social status in Kumo would also shape his character. If he was seen as a valuable asset from the start, he might have a more confident and perhaps even arrogant side to his personality, or if he was treated with suspicion because of his connection to Konoha in some way, he could be more of an outcast with a determination to prove himself worthy of Kumo.