One idea could be Ichigo crossing over into a world of gods and immortals where he has to learn their powers to save his own world. He could start as an outcast among them due to his different nature but gradually earn their respect.
The unique powers of Ichigo are a big factor. His Hollow - influenced abilities and Bankai form are not like anything in the RWBY universe. This brings a fresh and exciting element to the crossover. It's like introducing a whole new set of combat mechanics.
One plot idea could be Ichigo struggling to control his new dark godlike powers. He might accidentally harm his friends and then has to go on a journey to master them. Another could be that he is hunted by a powerful organization that fears his new powers.
His sense of justice could be refined. Dealing with different cultures and power dynamics in the crossover world, Ichigo would have to reevaluate what is right and wrong. This would lead to a more complex and nuanced view of justice for him. For example, if the gods have a different moral code, he would need to decide whether to abide by it or follow his own instincts.
One interesting concept could be the new powers Ichigo might gain in the crossover. For example, he could combine his existing Soul Reaper powers with those from the other crossover element in a unique way, like having a new type of Zanpakuto ability.
One idea could be Ichigo getting transported to a different dimension where he meets various female characters from different anime. They all fall for his unique powers and his sense of justice. For example, he could meet a magical girl who is intrigued by his sword skills and a strong - willed ninja girl who admires his courage.
One idea could be that Mugetsu Ichigo finds himself in an alternate universe where he has to team up with his other - self from that universe to defeat a powerful new enemy. Maybe this enemy has the ability to nullify his Zanpakuto powers, forcing him to rely on new and creative combat strategies.
Maybe in a Fullbring Ichigo crossover fanfiction, Ichigo's Fullbring could somehow get mixed up with a magical artifact from another fictional realm. This causes him to gain new and unpredictable powers. He then has to journey through different dimensions to find a way to control these powers while also being chased by powerful enemies who want the artifact for themselves.
One idea could be Ichigo being transported to a different anime world where he meets a harem of characters from that world. For example, if he ended up in the Naruto world, he could encounter female ninja who are intrigued by his unique powers and personality. Another plot could involve a magical spell that accidentally creates a harem situation for Ichigo in his own Bleach world, with various female characters suddenly having strong feelings for him. Maybe there's a time - travel element where Ichigo goes back in time and gathers a harem of historical figures with spiritual powers.
One plot idea could be that Ichigo somehow gets transported to the FMA world. He might initially be confused by the alchemical rules but then use his Soul Reaper powers in unique ways. For example, his Zanpakuto could be seen as a form of alchemical weapon, and he could fight alongside the Elric brothers against the homunculi. Another idea is that the Philosopher's Stone has some connection to the Hollow within Ichigo, and characters from both universes have to work together to prevent a catastrophic event.
One idea could be that Ichigo discovers he has hidden Quincy powers that are much stronger than he thought. This could lead to him having to train with Quincy mentors to control it, while also dealing with his Soul Reaper duties.