Renji would be a key character. He has a long - standing relationship with Ichigo (in this case female Ichigo). He would be torn between his loyalty to the Soul Society and his feelings for Ichigo. Another character could be Yoruichi. She is wise and might be the one to figure out the real reason behind Ichigo's betrayal. And Chad, who would be saddened by Ichigo's actions and might try to talk some sense into her.
Well, Uryu could be involved. He might initially be suspicious of female Ichigo's actions before the full - blown betrayal is revealed. Orihime would also be part of it. Her kind heart would make her try to reach out to female Ichigo and understand why she has turned against them. And of course, Kenpachi. His reaction to the betrayal would be more of an angry 'let's fight' kind of response as he doesn't tolerate traitors.
There could be Byakuya. He would be shocked and disappointed by female Ichigo's betrayal as he might have seen her as a promising comrade. Also, Rukia. Since she and Ichigo have a special bond, her reaction to Ichigo's betrayal would be very emotional. And then there's Aizen. He could be the one who tempted or manipulated female Ichigo into betraying, seeing her as a useful pawn in his grand schemes.
His friends Orihime and Chad would probably be main characters. Orihime could be very motherly towards baby Ichigo, always making sure he's comfortable. Chad would be the strong protector, making sure no harm comes to the baby.
Well, perhaps in the fanfic, female Ichigo betrays her allies because she has been brainwashed. Some sort of evil entity or powerful Quincy could have gotten into her head and made her believe that her friends are the real enemies. So she begins to pass on their secrets and even attacks them, leading to a lot of chaos and heartbreak among her former friends.
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.
In this fanfiction, characters like Luffy from One Piece might be involved. Luffy's carefree yet determined nature would contrast with Ichigo's new god - like presence. Also, characters from the Bleach universe itself could have new relationships with Ichigo. For instance, Aizen might see Ichigo's godhood as a threat or an opportunity, leading to a complex plot development.
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.
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.
Obi - Wan Kenobi is also a potential character. A body swap with Ahsoka would lead to some comical moments as well as some deep character exploration. Obi - Wan would have to handle Ahsoka's more impulsive nature, and Ahsoka would get to experience Obi - Wan's calm and collected Jedi demeanor.
Ichigo himself is obviously a common character. And then there are often female characters like Orihime and Rukia who are frequently part of his harem in fanfics.
Well, Sasuke could be one of the main characters involved. Since he has a complex relationship with Naruto, he might play a role in the betrayal, either as a part of the group that betrays Naruto or as someone who is conflicted about the situation. Sakura could also be involved. She has her own opinions and relationships within the Naruto universe, and she may be part of the group that turns against Naruto for some reason.
Ichigo could meet Frodo Baggins. Frodo, being from a very different kind of world, would find Ichigo's situation strange. But they could bond over their shared sense of being out of place in some ways. Frodo could teach Ichigo about the importance of perseverance in the face of great odds, and Ichigo could protect Frodo from any potential threats in this crossover world with his swordsmanship.