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.
Rukia would probably be both amazed and a bit worried. Amazed at the new power Ichigo has, but worried about how it might change him. Chad would see it as a natural progression of Ichigo's power and be supportive. Orihime might be a bit scared at first, but then she would see the good in Ichigo's new form and try to encourage him.
Ichigo might initially be in shock. He could be unable to believe that Tsukishima, who might have been a friend or at least an acquaintance, has turned on him.
Orihime would probably be over - the - moon excited. She's always been a kind - hearted and emotional person. She would immediately start knitting baby clothes or making cute little charms for the baby. Chad would be very supportive as well. He would offer his strength to protect Rukia during her pregnancy. Uryu might be a bit more reserved at first, but deep down he would be happy for them. He might use his Quincy skills to create some sort of protective item for the baby.
Rukia would probably be very suspicious right away. She knows Ichigo well and would notice the strange changes in his behavior. She might try to confront him and figure out what's wrong.
Chad would be a very protective and gentle presence. He would be like an uncle to the baby, always ready to pick the baby up and play with it. His calm and strong nature would make the baby feel safe.
The Soul Reapers in the Soul Society would see Ichigo as a major threat. They would likely mobilize their forces to either capture or eliminate him. Captains like Byakuya would be disappointed as he had come to respect Ichigo to some extent, and now would see him as a traitor.
Rukia would probably be one of the first to be both shocked and amused. She might tease Ichigo a bit at first but then quickly get serious about helping him. Chad would be very accepting and offer his protection as usual. Uryu might be a bit more skeptical at first, thinking it's some kind of new Hollow trick. Orihime would be very empathetic and try to make Ichigo feel comfortable in his new form, maybe even offer to make some new clothes for him to fit his new body.
Rukia would be extremely shocked and disappointed. She has always seen Ichigo as a force for good, and seeing him side with Aizen, who is the main antagonist, would be a huge blow to her. She might try to talk Ichigo out of it at first, and if that fails, she could become his enemy.