Baldroy could develop his strategic thinking skills. When protecting Ciel, he can't just rely on his brute strength. He has to plan ahead, like setting up defenses around the manor or creating escape routes. This would transform him from just a cook - turned - protector to a more intelligent and capable guardian. He may also develop better relationships with the other servants as they all work together to protect Ciel, which further enriches his character.
A possible plot is that Baldroy defends Ciel from a powerful magician who wants to use Ciel for some dark ritual. Baldroy, being the loyal servant, stands in the way and manages to hold off the magician long enough for help to arrive. Another could be that Baldroy protects Ciel during a trip through a dangerous forest. He fends off wild animals and traps set by bandits. Also, he might protect Ciel from a slander campaign within the aristocratic circles. He could gather evidence to prove Ciel's innocence by using his network among the servants.
Ciel would likely become more protective. He has always been in a dangerous world, and now with a baby on the way, he'll do whatever it takes to safeguard his family. Lizzy, she might become more nurturing. She was already a strong character, but motherhood could bring out a softer, more patient side of her.
Ciel would likely become more cold - hearted. His experiences as a human, especially the trauma he endured, would be amplified by his new demonic nature. He might lose some of his remaining humanity, such as his sense of compassion.
Naruto might become more cautious. Dealing with the 12 - tails, which is likely extremely powerful, would force him to think before acting. He can't just rush in like he sometimes does.
Their relationship could develop into a mentor - mentee type. Hulk's vast experience in dealing with powerful foes could help Peter grow as a hero. Peter, in turn, could show Hulk the value of using strategy and intelligence in combat.
I'm not sure specifically as it depends on the fanfic, but common servants in the Ciel universe might include Sebastian. He is a very important servant to Ciel and often plays a crucial role in many situations.
Charizard may start off as just a powerful protector. But as the story unfolds, it could develop more patience. For example, when Ash makes some hasty decisions in dangerous situations, instead of just acting impulsively, Charizard learns to hold back and guide Ash more gently. This shows growth in its character.
Naruto's character can develop in his combat skills in a more nuanced way in fanfiction. Instead of just relying on brute force, he might start to master some ancient and forgotten jutsus to better protect the village. He also learns to control his emotions better during combat situations, understanding that a rash move could endanger the entire village.
Naruto would likely become more studious. Instead of just relying on his natural energy and willpower, he'd have to spend time in labs and studying books. His impulsiveness might decrease as he learns the importance of precision in scientific work.
If trained by Hashirama in a fanfic, Naruto's character would grow in several ways. Firstly, his confidence would be enhanced in a different way. Instead of relying solely on his own tenacity and the power of the Nine - Tails, he would have the knowledge and skills passed down from one of the most legendary shinobi. This would give him a new sense of self - assurance. Secondly, his sense of responsibility towards the village would expand. Hashirama founded Konoha, and Naruto would understand more about the roots and values of the village, thus becoming more committed to its long - term well - being. He would also be more open - minded, as Hashirama had a very inclusive view of the ninja world, and Naruto would adopt some of that perspective.