One interesting plot idea could be a story where Shirosaki and Ichigo are forced to team up against a new, powerful enemy that neither can defeat alone. This would require them to put aside their differences and learn to work together, leading to some tense and interesting character interactions.
A plot could revolve around Shirosaki somehow getting separated from Ichigo's inner world and having to navigate the real world. Ichigo then has to find a way to bring him back without causing chaos, and during this time, Shirosaki starts to see the world from a different perspective, changing their relationship in unexpected ways. Well, this would be a great exploration of both characters in a new setting.
One idea could be a story where Ichigo and Shirosaki are forced to team up against a new, powerful enemy that threatens both their existences. They have to learn to trust each other despite their differences.
Maybe in the fanfiction, there's a threat that only Ichigo and Unohana can face together. They have to combine their different fighting styles, with Ichigo's brute strength and Unohana's precise and deadly techniques, to overcome the enemy. For example, they might encounter a powerful Hollow that has the ability to nullify most spiritual attacks, so they need to rely on their physical combat skills and teamwork.
A plot could involve Ichigo being trapped in the Hollow world and having to find a way back. Along the way, he meets other Hollows with different personalities and motives, some of whom he befriends while others are enemies. He discovers secrets about the origin of Hollows and how it relates to his own powers.
One plot idea could be that Ichigo and Halibel are forced to team up against a new, powerful enemy that threatens both their worlds. They start off distrusting each other but gradually learn to respect and rely on one another's strengths.
One idea could be that their pregnancy is a result of some kind of magical or spiritual event in the Bleach universe. Maybe an ancient spell gone wrong or right, depending on how you look at it. For example, a spell that was meant to protect Soul Society actually ends up causing Rukia to become pregnant. Another plot could involve the two of them having to hide the pregnancy at first because it goes against some Soul Reaper rules or traditions. They then have to deal with the consequences of keeping it a secret while also preparing for the arrival of the baby.
One plot idea could be that Ichigo and Eragon meet in a dimension that is a cross - between their two worlds. They have to team up to fight a common enemy that is threatening both of their universes. Their different powers, Ichigo's Soul Reaper abilities and Eragon's dragon - riding and magic, would make for an interesting combination in battles.
Another plot could be that an ancient evil force targets Femichigo because she represents a new and unknown power in the Bleach universe. Ichigo vows to protect her at all costs. Along the way, they discover secrets about their connection that were hidden by the Soul Society, and they have to fight against not only the external threat but also the political intrigue within the Soul Society.
One idea could be that Ichigo discovers new powers while recovering. Maybe his body is adapting to the intense battles he's been through, and he starts to have strange visions that lead him to unlock a hidden form of his Zanpakuto. This new power could be related to his inner Hollow or Quincy heritage in a unique way.
One idea could be that Ichigo has to train under Isane to learn more about healing techniques in the Soul Society. This would be a great way to explore their different skills and how they can learn from each other. Another could be that they team up to rescue a group of young Soul Reapers who are lost in a dangerous part of the Soul Society.
Well, a plot could revolve around Ichigo losing his powers again but Tier being the one to help him regain them in a very unique way. Maybe she has some ancient knowledge or a special connection to a power source that could potentially restore Ichigo's strength. And as they work on this, they start to form a bond that goes beyond friendship. Also, a fanfiction could explore what would happen if Tier was somehow injured and Ichigo had to protect her while also dealing with his own inner demons and the threat of other enemies in the Bleach universe.