The characters in DxD would be quite shocked at first. Ichigo's appearance and his powers are so different from what they are used to. For example, Rias Gremory would probably be intrigued by Ichigo. She might try to form an alliance with him, seeing his potential as a powerful ally. Issei, being the main character in DxD, would likely be both jealous and in awe of Ichigo's abilities, and might challenge him at first but then learn from him over time.
At the start, Ichigo would be defiant. He would not show any fear in front of Aizen. He might taunt Aizen, trying to get him to reveal his true intentions. As time goes on, he would start to feel a sense of isolation, but this would only strengthen his resolve. He would use his inner Hollow powers more freely, as he has no other option. He would also be constantly thinking about ways to turn the tables on Aizen and escape, and would be ready to take on any challenges that come his way during his captivity.
Ichigo would likely be defiant. He's a fighter and would not easily submit to Aizen. He'd probably be constantly looking for a way to escape and would be sizing up Aizen's every move, trying to find a weakness.
Ichigo would also experience a period of sadness. He values his relationships, and when one is broken through betrayal, it would hurt him deeply. He might isolate himself for a while, brooding over what happened. But ultimately, he would use this experience to become stronger. He'd learn from it and be more cautious in future relationships, while still maintaining his core values of loyalty and trust.
Some characters might be shocked at first. For example, her close male friends might feel a bit betrayed or confused, especially if they had a certain type of relationship with her when they thought she was a boy. But then they could come to accept and support her.
Ichigo might go into a state of self - reflection. He would wonder if there is something he has unknowingly done to cause this. He would try to analyze his past actions during the time travel. He might isolate himself from his so - called betrayers for a while to think things through. But ultimately, he would not give up on his friends. He would strive to find a way to regain their trust and set things right, because he values his relationships with them deeply.
Ichigo could be a game - changer. His Hollow - like powers might be mistaken for some sort of demonic or otherworldly ability in the Highschool DxD setting. This could lead to both misunderstandings and interesting interactions with the characters there.
One possibility could be that Ichigo's powers would make him a very unique and powerful character in the Highschool DxD universe. His zanpakuto abilities and high - level combat skills could give him an edge in the battles against the devils and other supernatural beings in that world.
A fanfiction could focus on Ichigo attending the school in Highschool DxD. His presence would surely disrupt the normal balance. He might not be interested in the whole 'devil' and 'angel' thing at first, but gradually get involved. He could also introduce some of his Soul Reaper training methods to the students there, which would be very different from what they're used to.
First, you need to understand the characters well. For Ichigo, know his personality traits like his determination and his sense of justice. For the Highschool DxD characters, understand their hierarchies and their goals. Then, come up with a unique plot. It could be a battle - oriented story where Ichigo and the DxD characters fight a powerful enemy together. Or it could be a more slice - of - life story where Ichigo adapts to the strange new world of DxD.