One possible plot could be that Ichigo is somehow tricked by Aizen. Maybe Aizen convinces Ichigo that by joining him, he can gain greater power to protect his friends in a different way. Ichigo, being naive in some aspects, might fall for this and start following Aizen's lead. This would lead to a huge shift in the power dynamics in the Bleach universe as Ichigo is a very powerful character.
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 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.
In 'ichigo and aizen lemon fanfiction', the focus is usually on the dynamic between Ichigo and Aizen. It might play with the idea of their rivalry in a more intimate or emotional context. This can add new layers to their characters. However, not all such fanfictions are well - written. Some might over - emphasize the 'lemon' aspect and lose the depth of the characters' relationship.
One idea could be that Aizen kidnaps them to use Ichigo's power and Rukia's knowledge of Soul Society for his own dark plans. He might want to study Ichigo's unique Hollow - Shinigami powers up close and use Rukia as a bargaining chip with Soul Society.
Aizen ended up being confined and his powers were controlled. He was no longer a threat. This conclusion came after a long and intense battle, showing that justice prevailed in the Bleach universe.
Aizen might be motivated by power. Ichigo has a very unique power set that Aizen may want to harness for himself. And Rukia, being from Soul Society, could be used as a way to gain information or leverage against Soul Society.
One thing that makes it special is the unique combination of two very distinct characters. Ichigo is the hero with a strong sense of justice, while Aizen is the complex villain. In the fanfiction, their interactions can be both thrilling and unexpected.
They are an interesting pairing because they are so different. Ichigo is a hero with a strong sense of right and wrong, while Fem Aizen has a more complex and often morally ambiguous nature. This contrast can lead to great character development and plot twists in fanfiction.
There's a fanfic called 'The Bond of Hearts'. It's set in an alternate universe where Ichigo and Orihime are childhood friends. It shows their relationship evolving over the years. It delves deep into their emotions and how they gradually realize their love for each other. The character development in this fanfic is quite engaging.