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.
In the past, their relationship might start with a lot of mistrust. But as they face challenges together during time travel, like dealing with a time - traveling dark wizard, they begin to respect each other's abilities. For example, Ginny's quick thinking and Draco's knowledge of certain spells become assets. This respect slowly turns into a tentative friendship as they rely on each other more.
The original series has a certain pacing and development for their relationship. But in the fanfiction, the Arrancar aspect of Ichigo could speed things up. For example, Arrancar Ichigo might have a more primal, possessive side towards Rukia. This could lead to a more passionate and tumultuous relationship. Also, they would face different external threats and challenges because of Ichigo's new form, which would force them to rely on each other in new ways and thus change how their relationship develops.
In a time - travel situation, Orihime could have a chance to understand Ulquiorra better. She might see his past and the events that shaped him into the being he is in their original timeline. This new understanding could lead to a deeper emotional connection between them. She could start to see him not just as an enemy but as a complex being with a tragic past, which would change the way she interacts with him.
In earlier time periods, like the medieval times of the wizarding world, their relationship might be more formal at first. They'd be outsiders in that time, so they'd rely on each other more. Fleur's Veela charm might be seen as more of a novelty or even a threat in that era, which could make Harry more protective of her. This would strengthen their bond.
In the past, their relationship could be shown as it was originally, full of rivalry yet an underlying respect. When they travel to the future, they might see how their actions in the past have influenced the current state of the ninja world. For example, if their enmity led to certain clan rivalries still existing. They could then work towards mending those relationships.
When traveling through time, they may encounter versions of themselves or their families at different ages. For instance, meeting their younger or older parents could give them new perspectives on their own relationship. They might learn things about their families' pasts that change the way they interact with each other in the present - day of their original time.
In a time - travel scenario, their relationship could develop more slowly. Since they are from different times, they might not understand each other's motives and values at first. But as they spend more time together, they could learn from each other. For example, Itachi could teach Naruko about the history and traditions of the Uchiha, while Naruko could show Itachi a more carefree and hopeful side of life.
It might develop through a series of battles and near - death experiences. For instance, if they are in a fight against a common foe and Hollow Ichigo saves Rukia's life. This act could make Rukia reevaluate her view of him. Similarly, if Rukia shows kindness or understanding towards Hollow Ichigo in a moment when he least expects it, it could thaw his cold exterior towards her, gradually building their relationship.
If they travel to the past, Kakashi might see Sakura in a new light. In their original time, he saw her as a student, but in the past, she could show different skills and a more mature side, which could make him respect her more as an equal. Their relationship could become more of a partnership rather than a teacher - student dynamic.
It could also develop more complicatedly. Suppose they travel to a future where one of them has made a big mistake in the fight against the Night King. This could create mistrust or a power struggle between them. Maybe Daenerys blames Jon for something that went wrong in the future battles, and they have to work through that while still trying to deal with the Night King threat.