Ichigo's power might be enhanced or changed. For example, if they travel to a time when the Hollow and Soul Reaper powers were more intertwined, he could gain a new form or ability. His Zanpakuto might also have different properties. Unohana's healing powers could be affected too. She might find that in some past or future time, her healing abilities are either more potent or restricted, depending on the state of the Soul Society at that time.
Ichigo is often headstrong and driven by his sense of justice. Unohana, on the other hand, is more reserved and has a deep well of knowledge. Their personalities would likely create a dynamic where Ichigo might initially be a bit frustrated by Unohana's calm approach, but gradually learn to appreciate it as he realizes the wisdom behind it.
I'm not sure if there is such a specific fanfiction. Fanfiction can cover a wide variety of scenarios, but this particular one might be a bit rare or not in line with the general tone of the original work. You could try searching on some major fanfiction websites to see if it exists.
Fanfiction with such themes may not be suitable for a wide audience, and it's better to focus on more positive and family - friendly fan - created works about Ichigo and Unohana.
In a more complex way, their relationship could be one of growth. Unohana's calm and collected nature could influence Ichigo to be more patient. At the same time, Ichigo's bold and fearless attitude could inspire Unohana to be more adventurous in her approach to things. This mutual influence could lead to a deep and meaningful relationship that evolves as they face different challenges together in the fanfiction.
There might be some stories where they team up to fight a powerful enemy. For example, in a fan - created scenario, they could join forces against a new Hollow threat that is stronger than any they've faced before. This would show their combat skills and how they might work together.
One possible plot development could be that they initially keep their relationship a secret due to their different positions or the rules within their world. Then, as they grow closer, they face challenges together, like dealing with enemies who might try to use their relationship against them.
Maybe in the fanfiction, there's a threat that only Ichigo and Unohana can face together. They have to combine their different fighting styles, with Ichigo's brute strength and Unohana's precise and deadly techniques, to overcome the enemy. For example, they might encounter a powerful Hollow that has the ability to nullify most spiritual attacks, so they need to rely on their physical combat skills and teamwork.
Perhaps the time travel is not what it seems. It could be a trap set by an unknown enemy. When Ichigo and Unohana think they are traveling through time to fix something, they are actually being led into a situation where they will be separated and used against each other. This would create a lot of drama and conflict in the fanfiction.
Perhaps a story where Ichigo and Unohana are on a joint mission. They are forced to rely on each other's skills. Unohana's calm and calculating nature could complement Ichigo's more impulsive fighting style. They might face a powerful enemy that requires both of their powers combined to defeat, leading to a deeper understanding and respect between them.