Maybe in a fanfic, the master - slave relationship is formed due to a special circumstance. Like a Quincy being captured by a Soul Reaper and instead of killing the Quincy, the Soul Reaper makes the Quincy their slave. The Quincy then has to learn about Soul Reaper culture and ways while secretly planning their escape, but over time starts to respect the Soul Reaper's code and develops a complex relationship with their master.
One idea could be that a powerful Soul Reaper takes on a young and inexperienced one as a sort of apprentice in a master - slave relationship. The master could teach the slave about different zanpakuto techniques and the ways of the Soul Society. For example, they could go on missions together where the master protects the slave at first but gradually lets the slave take on more challenges.
Perhaps a 'bleach school fanfic' could focus on the relationships between students. For example, two characters who are normally rivals have to team up for a project. They slowly learn to understand and respect each other's abilities. Or it could be about a group of students trying to solve a mystery that is plaguing the school, like strange disappearances that seem to be related to some dark spiritual force.
One idea could be a dragon from a hidden realm in the Bleach universe emerging and forging an alliance with Ichigo. The dragon could have unique powers that help Ichigo in his battles against the Hollows. For example, it might be able to breathe a special type of reiatsu - infused fire that can purify Hollows more effectively than a normal Soul Reaper's sword.
A cool plot for a 'bleach sleepover' fanfic could involve the characters from different factions in 'bleach' coming together for a sleepover. For example, the Shinigami and the Arrancar. At first, there's tension, but as the night progresses, they start to understand each other better. They could play games like truth or dare, which leads to some really interesting character revelations and unexpected alliances forming. This could also set the stage for future interactions in the 'bleach' universe outside of the sleepover.
Ichigo and Zangetsu could be an interesting pair in a master - slave fanfic. Zangetsu, as the inner spirit of Ichigo's zanpakuto, has a sort of master - like relationship over Ichigo in terms of teaching him about his power. They could be in a situation where Zangetsu is more dominant in guiding Ichigo's growth, like a strict master with a somewhat rebellious slave.
One idea could be that the humans find a way to access the Soul Society without permission, leading to chaos as they start to explore and misunderstand the different realms. Maybe they accidentally release some dangerous Hollows in the process.
A possible plot for a 'bleach swinging pendulum fanfic' could be centered around the idea of moral pendulum swings. Characters who were once considered 'good' in the Bleach world start to question their actions and motives. For example, Soul Reapers who have always been about maintaining order might find themselves in situations where their traditional methods seem cruel or unjust. This could lead to internal conflicts within the Soul Society. On the other hand, some Hollows might experience a change towards redemption. The story could explore how these moral shifts affect the relationships between different factions and the overall dynamic of the Bleach universe.
One idea could be that Naruto is turned into a vampire slave against his will. He has to struggle between his ninja values and the new vampiric instincts. Maybe he tries to find a way to break the slave bond while still using his vampire powers for good, like protecting the Hidden Leaf from new, more sinister threats.
One idea could be to explore an alternate timeline where Ichigo never became a Soul Reaper. Maybe he lives a normal life, but strange spiritual events still occur around him, drawing him into the world of the Hollows and Soul Reapers in a different way. Another idea is to focus on a side character, like Uryu, and tell a story from his perspective during a major arc that we didn't see much of in the original series. For example, his experiences during the Arrancar arc when he was off on his own missions.
One idea could be a story where a character from 'White' falls in love with a character from 'Orange' in a world that has elements of 'Bleach'. For example, they could meet in a spirit realm similar to that in 'Bleach' and their love story unfolds while dealing with the unique powers and politics of their respective worlds.
One interesting plot idea could be Karin discovers she has a new spiritual power that Toshiro helps her control. They go on a journey together to figure out the origin of this power, facing various Hollows along the way. This would bring them closer as they rely on each other's skills.