Ichigo might become more cautious. In his own time, he's often impulsive, but going back in time and seeing the consequences of actions he hasn't even made yet could make him think twice. He might also gain a deeper understanding of the history of the Soul Society and his own place in it. Kisuke, on the other hand, could become more open. He usually has his own secrets, but in the past, he might be forced to be more transparent with Ichigo and others in order to survive and complete their mission. For example, he might have to reveal some of his early experiments or knowledge that he's been keeping to himself.
Sam might become more assertive in his beliefs. When they go back in time, he could encounter situations where his modern - day knowledge about certain supernatural entities clashes with the beliefs of the past hunters. Instead of being swayed, he would stand his ground and try to convince others. As for Dean, he could become more empathetic. In the past, he might meet versions of his family or friends in difficult situations that he didn't fully understand before. This would make him more understanding and kinder towards others in similar situations in the present.
In this fanfiction scenario, their relationship could be more like brothers in arms. They both have regrets from their original timelines. They would rely on each other more deeply. Obito might open up to Naruto about his past and his love for Rin much earlier. Naruto could also share his own insecurities and how he overcame them in the future. This would create a stronger bond between them, and they would fight side by side more effectively against the common enemies, whether it's the Akatsuki or other threats to the ninja world.
If they travel to a time when the Quincy and Soul Reapers were at peace, their relationship could develop in a more carefree way. They could explore the different cultures together without the threat of war. However, if they go to a time when there was a great divide between the two groups, they might have to hide their relationship or even be on opposite sides at first. But as they discover the truth behind the conflict, they could work together to bridge the gap, which would enhance their relationship. In a time closer to their own but with some changes, like if Ichigo was more powerful from the start, Rukia might have a different kind of admiration for him, and their relationship could shift from a more mentor - student type to a more equal partnership faster.
If Levi travels back in time, his character could develop more compassion earlier. In the original timeline, he had to go through a lot of hardships to become more empathetic towards his comrades. But if he goes back, knowing what he knows now, he might start showing more care from the beginning. For example, he could be more patient with new recruits instead of his usual tough - love approach.
Naruto might become more introspective. Instead of always charging forward, he would start to analyze his actions in each loop. Sasuke, on the other hand, could become more open. He would see Naruto's determination in different loops and start to question his own aloofness.
Bilbo might become more adventurous and less home - bound. His time - traveling experiences could make him bolder. For instance, he might be more willing to take risks in new situations. Aragorn, in contrast, could gain a deeper understanding of the long - term consequences of his actions. He would see how different choices in the past have led to the present situation in Middle - earth.
His character could develop a sense of urgency. Knowing that he died in his original timeline, he would want to make the most of his second chance. He might become more of a leader, taking charge in situations where he previously would have held back. He could also become more empathetic, as he has seen the consequences of his actions in the past life.
She might become more confident in her earlier years. In the original story, Arya faced many hardships that made her grow in a certain way. But if she goes back in time, having the knowledge of future events, she could be bolder in her actions and decisions from a young age. For example, she might be more assertive in dealing with Sansa when they were kids, and not let Sansa's girly ways get to her as much.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Kisuke x Ichigo time travel' in their search bars, and you'll get a list of relevant stories. Some might be really well - written with interesting plot twists and character developments.
Ichigo's character may develop by becoming more confident in his powers. In the past, he has a chance to redo things and learn from his mistakes. He could become more strategic in battles, using his transcendent abilities more effectively.