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.
A really cool plot could be set in an alternate universe where Ichigo and Halibel are from the same clan. They grow up together and are trained to be warriors. However, a rift forms between them when they have different views on how to protect their clan, leading to a complex and emotional story of friendship, betrayal, and redemption.
Perhaps a fanfiction where Halibel has lost her memory and Ichigo finds her. He decides to help her regain her memories while also protecting her from those who might want to take advantage of her in this vulnerable state. As they spend time together, they form an unexpected bond.
Maybe in the fanfiction, Ichigo gets lost in Hueco Mundo and Halibel finds him. Instead of attacking, she decides to help him find his way back. During their journey, they encounter various challenges and secrets about Hueco Mundo are revealed to Ichigo through Halibel. This could lead to a new understanding between the two species they represent.
Perhaps a plot where Ichigo accidentally ends up in Hueco Mundo near Halibel's territory. She initially sees him as a threat but then discovers that he has no intention of harming her or her fracciones. This could lead to an exploration of their different worlds and cultures within the Bleach universe.
Well, for a Bleach Halibel x OC fanfiction, a plot could revolve around the OC being a time - traveler. The OC travels back in time and meets a younger Halibel before she became an Espada. This could change the course of Halibel's life and their relationship. Or, the OC could be a musician in the human world whose music can reach the spiritual realms. Halibel hears this music and is drawn to the human world to find the source, which is the OC. Also, the OC could have a special ability to communicate with water, just like Halibel has an affinity with water - based attacks. They could bond over this shared connection.
A plot could involve Halibel getting injured and being found by Ichigo. He takes her in and nurses her back to health. During this time, they have a chance to really talk and get to know each other on a deeper level. Their different worlds collide as they start to develop feelings for one another, but they also face challenges due to their different allegiances.
Well, a plot could involve a power - sharing situation. Maybe there's a power - draining curse in Hueco Mundo that affects both of them. In order to break it, they have to combine their powers in a way they never thought possible. This journey of trying to break the curse could make them see each other in a new light. They could also be involved in a mystery where they have to figure out who is behind a series of disappearances in their territory. Working together on this mystery could bring them closer.
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.
Their powers could be combined in a way where Ichigo's Zanpakuto spirit, Zangetsu, and Halibel's water - based powers merge. For example, Ichigo could gain the ability to use water - enhanced slashes that have the cutting power of his normal attacks along with the fluidity of Halibel's water attacks.
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 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.
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.