For writing compelling characters in a Fullbring Ichigo crossover, it's important to give them flaws. Ichigo has his temper and tendency to rush into things. For the crossover characters, give them believable weaknesses. Also, create relationships between the characters. Ichigo could form a mentor - mentee relationship with a more experienced character from another universe. Or he could have a friendly rivalry with someone who has similar powers but a different ideology. These relationships will make the characters more engaging and drive the story forward.
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.
There are quite a few good ones out there. For example, 'Beyond the Final Form' is a fanfic that not only explores Ichigo's new powers but also the lore behind his final form. It has a complex plot that involves different Soul Society factions reacting to Ichigo's transformation. 'The Final Form's Purpose' is another one where the author tries to give a deeper meaning to Ichigo's final form, like it being a key to a greater mystery in the Bleach universe.
Firstly, a good fanfic should stay true to the Bleach universe's rules and lore. Regarding Ichigo's final form, it should explain how he achieved it in a way that makes sense. It could be related to his Quincy, Hollow, and Shinigami powers. The character development is crucial. Maybe Ichigo has to overcome some self - doubt or fear associated with his new form. Additionally, the writing style matters. A vivid and engaging style can really bring the story of Ichigo's final form to life, making the readers feel like they are right there in the Bleach world, experiencing his transformation and the events that follow.
One idea could be exploring how Ichigo's hollow form affects his relationships with his friends. Maybe his hollow side makes him more aggressive towards them at first, but they gradually learn to accept and help him control it.
There might be a fullbring Naruto fanfiction where the concept of fullbring is incorporated into the Ninja world in a unique way. For example, fullbring abilities could be related to the different chakra natures. So Naruto, with his wind chakra, could have a wind - based fullbring that allows him to manipulate air currents in ways he couldn't before. This could lead to some really cool battle scenes and new strategies.
One interesting Naruto fullbring fanfiction could be one where Naruto discovers a new form of fullbring that combines his chakra powers with it in a unique way. For example, he might be able to fullbring out the essence of the Nine - Tails in a more controlled and powerful form.
Naruto himself is an obvious choice. His ability to adapt and his large amount of chakra could lead to some really cool fullbring combinations. He could bring out new and powerful forms that we've never seen before.
One possible plotline could be Naruto discovers he has a hidden Fullbring ability. He then has to learn to control it while still dealing with the threats in his own world. Maybe he uses it to fight stronger enemies like Madara in a new and unexpected way.