The Bnha universe's reaction would be mixed. Those who are into complex stories, like Todoroki, might study the relationships in Hamilton fanfiction. But others, like Mineta, might not be interested at all because it doesn't have much to do with his usual interests. Overall, it would depend on the individual characters' personalities and interests.
Some would be inspired. Characters like All Might might see Peter Parker's journey as similar to his own in some ways. Both are trying to do good in a world full of challenges. All Might could appreciate Peter's determination to protect his city despite having a normal life outside of being a hero.
For heroic - centric fanfictions, they would likely be disdainful. Since they oppose heroes, seeing stories that glorify heroes would annoy them. They might scoff at the idealized versions of heroes in those fanfictions.
He'd probably be shocked by the different power systems. Naruto is used to chakra and jutsus, while Bleach has spiritual energy and zanpakutos. So it would be a big change for him to read about.
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.
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.
Some of them could be entertained. For those who are more open - minded, like Yoruichi, she might find it fun to see the different interpretations of their world and the characters in it. However, others, like Byakuya, might be more critical and think that the fanfiction distorts the original values and stories of the Soul Society.
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.