For a Luffy Gear 5 fanfic, you could have a plot where Luffy's Gear 5 form is somehow corrupted by a dark force. He starts to lose control of his actions and becomes a danger to his friends. His crew has to find a way to purify his Gear 5 power. Another interesting idea is that Luffy discovers that Gear 5 has a hidden ability that allows him to travel through time briefly. He uses this ability to go back and change a crucial event in the past that has far - reaching consequences for the present. This could lead to a whole new set of adventures and challenges for Luffy and his crew.
One interesting idea could be exploring new abilities Luffy discovers within Gear 5 that he hasn't shown in the official story yet. For example, he might be able to manipulate his surroundings in even more creative ways, like turning the air into rubbery substances to create platforms or traps.
In some One Piece Luffy Gear 5 fanfiction, there could be the idea of Luffy sharing his Gear 5 power with his crewmates temporarily. This would not only make for some cool team - up attacks but also show the deep bond within the Straw Hat crew. Also, a fanfiction might explore how Luffy's Gear 5 affects his relationship with other pirates or the World Government. Maybe it makes him an even bigger target or maybe it causes some pirates to want to ally with him out of fear or respect.
One idea could be that Dragon discovers Luffy's true potential during a battle against a common enemy. Maybe Dragon secretly aids Luffy without him knowing, guiding the wind or weather to give Luffy an advantage. This would add an interesting layer of mystery to their relationship within the fanfic.
One idea could be exploring how Naruto discovers a new way to enter Gear Second that gives him even more power. Maybe he combines it with a new jutsu he's been working on.
One idea could be that Luffy travels back to the time when Gol D. Roger was still alive. He could meet the Pirate King and learn some of his secrets. Maybe Roger gives him a hint about the One Piece that changes Luffy's understanding of his journey.
One idea could be that Luffy accidentally discovers a secret about a Celestial Dragon that could change the power balance in the One Piece world. He then has to decide whether to expose it or use it to his advantage.
One idea could be that Percy discovers a new kind of Sacred Gear during one of his quests. Maybe it has the power to control water in a completely different way than his normal abilities. Another could be a crossover where Percy and a character with a Sacred Gear team up to defeat a common enemy that neither could face alone.
One idea could be a crossover where the characters from Metal Gear Rising have to adapt to the world of RWBY. For example, Raiden could team up with Ruby and they could share their combat skills. Maybe Raiden teaches Ruby some advanced sword techniques, while Ruby shows Raiden how to use Dust in combat.
Luffy Gear 5 Fanfic: In the heart of a new island, Luffy stood tall in his Gear 5 form. His body pulsed with a vibrant red energy as he faced the powerful new foe. 'I won't let you harm my friends!' he roared. With a swift motion, he stretched his arm like a rubber band, then snapped it forward, sending a shockwave of Haki towards the enemy. The foe tried to dodge but was caught in the blast, sent flying backwards. Luffy then bounced around the battlefield, his movements a blur, leaving trails of light as he continued his attack.
One interesting plot idea could be that they go on a special adventure to find a lost ancient island that only Robin can decipher the clues to reach. And along the way, Luffy's unwavering determination and Robin's knowledge work together to overcome various obstacles like strange sea creatures and difficult terrains.