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.
Ichigo might go into a state of self - reflection. He would wonder if there is something he has unknowingly done to cause this. He would try to analyze his past actions during the time travel. He might isolate himself from his so - called betrayers for a while to think things through. But ultimately, he would not give up on his friends. He would strive to find a way to regain their trust and set things right, because he values his relationships with them deeply.
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.
A few might be angry. If the fanfiction shows them in a negative light or changes their backstory in a way they don't like, they could get really mad. For example, if a character with a noble past is made into a villain in the fanfiction, they'd be furious.
There could be friends who are initially shocked. They might not have expected Ichigo and Senna to start a family so soon. But after the initial surprise, they would come around and offer their congratulations. Maybe they would even share their own experiences of having children or being around pregnant friends.
Luffy from One Piece is also a common pairing. Luffy's carefree and adventurous nature combined with Ichigo's more serious and duty - bound personality would lead to some really fun and unpredictable interactions. They could be on a quest in a crossover world, with Luffy's devil fruit powers and Ichigo's Soul Reaper abilities working together in strange and amazing ways.
Uryu could also be a main character. He might be initially skeptical of Ichigo's transformation into a dragon god but then come to respect and even rely on his new powers in battles against common enemies. His Quincy abilities could contrast with Ichigo's dragon god powers, creating interesting interactions between them.
The Ichigo 100% anime doesn't have the exact same ending as the manga. There are variations in how the story wraps up, which could be due to various factors like creative decisions or adaptation constraints.
Rukia could be a great character to pair with Ichigo. Since they have a strong bond in the original series, in the fanfiction, she could follow him into the other world or be summoned there later. Their combined power and friendship would make for an interesting dynamic as they face new challenges.