One interesting crossover could be Edward Kenway finding himself in the One Piece world. He might be intrigued by the Devil Fruits and try to get his hands on one for his own gain. Maybe he'd team up with Luffy's crew for a while, sharing his sailing and combat skills.
In a fanfiction crossover, Edward Kenway's stealth and assassination skills could be a great asset to the One Piece characters. He could teach them how to move more quietly and efficiently during battles. For example, he could train Zoro in the art of silent approach before striking, which would give Zoro an edge in his sword - fighting.
When it comes to navigation, Nami would be interested in Kenway's knowledge of different sea routes and hidden islands. Kenway could learn from Nami about the unique weather patterns in the One Piece world. Also, Chopper would be curious about Kenway's health and any medical knowledge he has from his time as a pirate. Kenway, in turn, would be entertained by Chopper's cute and innocent nature.
One interesting crossover could be Batman finding himself in the One Piece world. He might be initially confused by the Devil Fruits and the strange sea creatures. Maybe he teams up with Luffy to take on a common enemy who has both high - tech weapons like in Gotham and the strange powers of the One Piece world. Another could be Robin or Nami being interested in Batman's gadgets and trying to reverse - engineer them.
In a One Piece - Justice League fanfiction, perhaps Zoro could cross paths with Batman. Zoro's swordsmanship and his sense of justice might align with Batman's detective skills and his own brand of justice. They could exchange combat techniques and strategies, and Zoro could learn a thing or two about stealth from Batman.
One possible interesting crossover could be having Luffy from One Piece end up on the Rosario Vampire campus. His carefree and fearless attitude would surely stir things up among the various supernatural beings there. He might mistake some of the vampire or monster students for strange new island inhabitants and try to befriend them in his usual enthusiastic way.
One interesting crossover could be Goku arriving in the One Piece world and teaming up with Luffy to fight a powerful enemy. Goku's incredible strength and combat skills combined with Luffy's Devil Fruit powers would make for an epic battle. Another could be Goku teaching the Straw Hats some of his martial arts techniques, which would enhance their fighting abilities in their own adventures.
One interesting crossover could be the Hogwarts students going on a magical adventure in the world of One Piece. Maybe they could use their magic to help the Straw Hat crew in battles against the Marines or other pirates.
One interesting crossover could be Naruto characters joining the Marines in the One Piece world. For example, Naruto with his determination and powerful jutsu could become a unique Marine recruit. He might use his shadow clone jutsu to handle multiple tasks on a ship or in battle. Another could be a team - up between Luffy and Naruto against a common enemy that threatens both their worlds. They could combine Luffy's stretching abilities with Naruto's Rasengan for a super - powerful attack.
One interesting crossover could be the characters' abilities. For example, Percy's control over water could interact in unique ways with the ocean -centric world of One Piece. Maybe he could team up with Luffy and help him cross the Calm Belt more easily.
Begin by creating a conflict that involves both Edward and Connor. It could be a new Templar threat that has roots in Edward's time and resurfaces in Connor's. Develop their characters further by giving them internal struggles. Maybe Edward is haunted by his past actions as a pirate, and Connor is struggling with his identity as an Assassin in a changing world. As you write, keep the pacing right. Alternate between action - packed scenes and more reflective moments. And most importantly, let your love for the Assassin's Creed series shine through in your writing.
A fanfiction could be about family ties. Maybe Connor discovers he has a distant relative who was part of Edward's crew. He sets out to find this person and in the process, uncovers more about his family's past. Along the way, he meets Edward's ghost or some kind of spiritual manifestation of him. Together, they work to protect a hidden Assassin stronghold from the encroaching Templars.