In such a fanfic, the captured scenario could lead to some great character development. For Ichigo, it might be a test of his strength and resolve. He could discover new aspects of his powers while trying to escape. Aizen, being captured, might show a different side of himself, perhaps a more desperate or calculating side. Irukia might use his friendship with Ichigo to boost their morale. The interactions between them would be filled with tension and drama, as they deal with the captivity and whatever threats are associated with it.
Well, in a fanfic where these characters are captured, there could be a lot of intense situations. Maybe Aizen, being the crafty character he is, would try to manipulate the situation to his advantage. Ichigo, on the other hand, would probably be looking for a way to break free and fight back. And Irukia might be using his cool - headedness to assess the situation and come up with a plan. They could also be forced to work together against a common enemy in the fanfic, which would be an interesting dynamic considering their different personalities and powers.
A plot twist could be that the place they are captured in is not what it seems. It could be a magical or illusionary prison created by an unknown force. This would make their escape much more difficult as they have to figure out the true nature of the prison. Also, it could turn out that their capture was a self - fulfilling prophecy. Maybe Aizen's actions in the past led to a chain of events that resulted in their capture, but in a way he didn't expect. And Irukia could be the key to their escape, but he doesn't realize it until later in the fanfic.
Ichigo would likely be defiant. He's a fighter and would not easily submit to Aizen. He'd probably be constantly looking for a way to escape and would be sizing up Aizen's every move, trying to find a weakness.
One possible plot could be Ichigo's struggle to escape Aizen's prison while also trying to figure out Aizen's true motives for capturing him. Maybe he discovers some dark secrets about Aizen's past during his captivity. Another plot could involve his friends trying to rescue him and the battles they face against Aizen's minions on their way to save Ichigo.
In this fanfiction, Ichigo might be held in a secret location by Aizen. Aizen could be planning to use Ichigo for some dark experiment or to gain his power. Maybe he'll try to manipulate Ichigo's Hollow side for his own evil purposes.
Maybe Aizen has created a false asylum as part of a new experiment. He lures Ichigo and Rukia into it, and they have to find a way to escape while also dealing with the illusions and traps Aizen has set up. In the process, they could learn more about Aizen's motives and past, and perhaps even find a way to defeat him once and for all.
One possibility is that the captains start to question their own beliefs and power levels. Ichigo, being a substitute Soul Reaper, is taking on Aizen, a very powerful foe. This could make the captains realize that there are other ways to gain strength beyond the traditional Soul Reaper training. They might also start to see Ichigo as a potential ally in future battles against greater threats.
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.
Well, one possibility is that Aizen somehow convinces Ichigo that his way is the only way to protect his friends. Maybe he shows Ichigo a false future where all his friends die if he doesn't side with Aizen. Ichigo, being desperate to save them, might then join Aizen, thinking he can change things from the inside.
In this fanfic, Katniss might face intense torture. The Capitol is known for its cruelty. They could use various methods to break her spirit, like starving her or subjecting her to mind - games. Maybe they'll try to use her as a tool to control the rebels, threatening to kill her if the rebellion doesn't stop.
In such a fanfic, Naruto might be subjected to various interrogations by Kumo. They could be interested in his Nine - Tails power. Maybe they would try to extract information about Konoha's secrets through him.