One idea could be that Hancock uses hypnosis to make her enemies see illusions of her army being much larger than it actually is. This would give her an advantage in battles without having to engage in full - on combat.
A fanfic could revolve around Hancock using hypnosis to teach the Kuja tribe some new skills or knowledge. For example, she hypnotizes the warriors to be able to quickly learn advanced combat techniques from other pirates she has encountered during her travels, which would enhance the tribe's overall strength and ability to protect themselves.
I'm not sure if there are extremely popular ones specifically focused on this concept. However, there are likely some out there in the vast world of fanfiction. You might need to search on dedicated fanfic websites like Archive of Our Own or FanFiction.net and use specific search terms like 'boa hancock hypnosis' to find relevant stories.
One idea could be a fanfic where Boa Hancock has to team up with her former enemies to face a greater threat. Maybe a powerful new pirate crew that is causing chaos in the Grand Line and she has to put aside her pride for the greater good.
A fanfic could explore a friendship between Boa Hancock and Domino. For instance, Domino visits Amazon Lily and is initially met with suspicion but through her interactions with Hancock, they develop a bond. They could exchange stories about their different experiences in the world.
One interesting idea could be how the concept of hypnosis is integrated into the Dragon Ball universe. Maybe it's used as a new form of combat strategy, where a character hypnotizes their opponent to lower their guard or make them perform certain actions against their will.
Perhaps a 'pokemon hypnosis fanfic' could involve a group of pokemon researchers who accidentally discover a form of hypnosis that can communicate with pokemon on a deeper level. They use this to learn more about pokemon behavior and intelligence. However, some unethical individuals try to use this for their own gain, leading to a conflict.
One interesting plot idea could be a villain using hypnosis to turn Naruto's friends against him. This would create a lot of internal conflict for Naruto as he has to figure out how to break the hypnosis and regain their trust.
One idea could be that a new enemy uses hypnosis to make the Dragonball characters forget their powers. So, they have to go on a journey to rediscover their abilities and defeat the enemy. It's a great way to show their growth and determination.
Perhaps in the fanfic, the hypnosis bloodline allows the user to enter people's minds and change their memories. The story could be about a character who uses this ability to rewrite the past of a village that has been corrupted by an evil force. However, they soon realize that changing memories has unforeseen consequences and they have to find a way to fix the mess they've created.
One idea could be a fanfic where Dracula uses hypnosis to teach the younger monsters at the hotel good manners. He hypnotizes them into believing that they are in a fancy etiquette school and they have to learn how to be polite to guests. This could lead to some funny situations as the little monsters try to be proper while still being their mischievous selves.
One idea could be that the OC is a new pirate who joins the Straw Hats. Over time, they develop a special bond with Nico Robin due to their shared interest in ancient history. Meanwhile, during an encounter with Boa Hancock, the OC manages to gain her respect in an unexpected way, like saving her from a new threat in the Grand Line. This could lead to a complex love triangle where the OC has to navigate their feelings for both strong - willed women.