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.
Rukia could be a character. She might come to Ichigo's rescue when she hears about his situation with the tentacles. She could use her own powers to freeze or cut through the tentacles. Another potential character is Uryu. He could use his Quincy skills to disrupt the energy of the tentacles. And there's also Orihime, who might use her shield - like abilities to protect Ichigo from the tentacles.
I haven't come across a fanfiction with that exact plot. Most fanfictions tend to focus on different aspects of the characters' relationships, like their adventures together or how they develop their powers. A plot like Ichigo getting Senna pregnant might be too extreme for the typical fanfiction writer, as it could deviate too much from the essence of the original story.
One possible fanfiction could be that Ichigo gets hurt while facing a new and extremely powerful Hollow. He might be caught off - guard during the battle, the Hollow's unique attack managing to pierce through his defenses and wound him severely. His friends then have to step in to protect him while he tries to regain his strength.
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.
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.
While the world of fanfiction is vast and full of creative and sometimes out - there ideas, this particular concept seems rather unorthodox. It's important to note that if such a fanfiction exists, it would likely be a very niche creation. And given the nature of the Bleach characters and their relationships in the source material, it's not something one would expect to find easily in the realm of fan - created stories.