Well, a Bankai R Ichigo Rukia fanfic can be really exciting. Usually, it delves deeper into the powers and relationships of Ichigo and Rukia during their Bankai states. The fanfic might explore new battles, their growth as characters, and how their bond evolves. It could also introduce new elements to the Bleach universe that the original series didn't fully explore.
Obviously, Ichigo is the central character in 'ichigo goes beyond bankai fanfiction'. But we can't forget about his mentor figures like Urahara. Urahara has always been a bit of a mystery and has a lot of knowledge about spiritual powers. He could be crucial in helping Ichigo understand and master his new powers. Then there are Ichigo's opponents. There might be new and powerful adversaries who are either threatened by Ichigo's new power or are trying to harness it for themselves. These opponents would also be important characters in the story.
One thing that makes a Bankai R Ichigo Rukia fanfic stand out is its unique take on their powers. Maybe it shows Ichigo's Bankai in a different light, perhaps with some new abilities or a different aesthetic. For Rukia, it could be the same, like her Bankai having some unexpected twists.
One interesting plot point could be Ichigo's new powers and how they change his battles. For example, he might have abilities that allow him to manipulate time or space in combat. Another could be the reactions of his friends and foes to this new level of power. His friends might be in awe or a bit worried about his newfound strength, while his enemies would likely be more fearful and have to come up with new strategies to face him.
Honestly, I don't know when the TYBW manga starts. But you could search manga databases or ask in manga enthusiast communities to get the details you need.
Naruto's bankai might incorporate his fox - like features. Given his connection to the Nine - Tails, his bankai could have a large, fiery fox form that enhances his speed and strength, much like how his Nine - Tails Chakra Mode works. His zanpakuto could also be related to the rasengan, perhaps having the ability to fire off rasengan - like attacks from the blade or using the spinning energy as a defensive mechanism.