One possible plot twist could be that Ichigo discovers he has a special power in the new world that is completely different from his Soul Reaper powers. For example, he might be able to control the elements, which would change the way he approaches challenges.
A really interesting plot twist could be that the inhabitants of the other world mistake Ichigo for a long - lost prophesied hero. But as he tries to live up to this role, he realizes that the prophecy has been misinterpreted and there's a much darker truth behind it. This would add a whole new layer of complexity to the story as he has to figure out how to deal with the situation without causing chaos or getting himself killed.
It could be a powerful wizard or sorcerer in the new world who sees Ichigo as a threat to his rule. Maybe Ichigo's presence disrupts the balance of power that this antagonist has carefully maintained.
One possible plot twist could be that Aizen has a hidden motive other than just causing chaos. Maybe he kidnaps Ichigo to use his unique powers for some sort of experiment. For example, he might want to extract the power of Ichigo's Hollow side to enhance his own strength or create a new type of Arrancar. Another twist could be that Aizen is being controlled by an even greater force, and Ichigo's kidnapping is part of a larger plan to draw out other powerful characters in the Soul Society.
The new world could be a medieval - style realm filled with knights, castles, and magic. Percy might find himself in the middle of a war between kingdoms, using his skills to survive. Maybe there are mythical creatures like dragons and unicorns there.
One possible plot twist could be that Ichigo struggles to control the Sharingan at first. Since he's not from the Naruto universe originally, the sudden addition of the Sharingan's powers might be overwhelming. He might accidentally activate it during battles in the Bleach world and it could give him an edge in seeing his opponents' moves more clearly, but also make him a target as it's an unknown power in his world.
Maybe Ichigo is secretly a girl because she's on a secret mission. In the fanfiction, she could be a spy or an undercover agent. Her guise as a boy has allowed her to infiltrate certain groups or places. When her true identity as a girl is discovered, it throws the whole mission into chaos, and she has to find a way to salvage it while dealing with the personal relationships that are affected.
One possible plot twist could be that Yoruichi's love for Ichigo is forbidden in the Soul Society. Maybe there are rules against such relationships between different 'classes' or species. For example, Yoruichi being an ex - captain and Ichigo being a human - turned - Soul Reaper - substitute. This could lead to a lot of drama as they try to hide their feelings from others.
One idea could be that the OC discovers they have a special power in the new world that is key to saving it from an ancient evil. For example, the power to control time, which is a very cool concept.
One plot twist could be that they face opposition from the Soul Society. Since Ichigo is a substitute Soul Reaper and Yoruichi has a complex history there, the elders might try to stop the marriage for political or traditional reasons.
A plot twist might be that Ichigo discovers some long - hidden family secret related to Byakuya during their marriage preparations. This secret could change the way he views Byakuya and their relationship, adding a layer of complexity and drama to the story. For example, it could be related to a past event that involved their ancestors.
One possible plot twist could be that Ichigo, now as a girl, has to deal with different power dynamics. Maybe her reiatsu (spiritual pressure) is affected in a new way. For example, it could become more refined or have a different color, which would attract different kinds of Hollows or Soul Reapers. Another twist could be in her relationships. Her friends might initially be shocked and not know how to interact with her. Uryu, for instance, might be more hesitant to be around her at first. Also, the Soul Society's reaction could be interesting. They might be suspicious of this change and think it's some kind of new threat or a trick by the Quincy. Overall, the story could explore how Ichigo's personality remains the same despite the physical change, but she has to adapt to the new social and power - related situations.