One idea could be a story about a young sailor who discovers a hidden island in the cold waters. He might find ancient secrets or magical creatures there.
A plot could revolve around a pirate crew that is forced to sail into the cold waters of Planetos due to being chased by a powerful navy. In these cold waters, they find an abandoned ship filled with treasures but also guarded by a terrifying sea monster. The crew then has to decide whether to risk their lives for the gold or flee.
An old seer who lives on an isolated island in the cold waters could be a main character. He has the power to foresee events related to the sea. People from all over come to seek his advice, and his interactions with those who visit could form the basis of the story.
One idea could be that the cold killer is a rogue ninja who was once a part of a secret Anbu - like organization in the Naruto world. They have a tragic past that made them turn cold - hearted. For example, they witnessed their entire clan being massacred by a powerful enemy. Another plot could involve the cold killer being hired to assassinate a major Naruto character, but during the mission, they start to question their own motives and actions when they learn more about the target. Maybe they find out that the target is not as bad as they initially thought.
One plot idea could be that Naruto, who is cold and distant after a difficult mission, crosses paths with Ino. Ino tries to break through his cold exterior using her mind - reading skills in a non - invasive way. Maybe she discovers that Naruto is feeling guilty about something that happened on the mission and she helps him come to terms with it.
One idea could be that Andu has a special ice - based jutsu that Naruto must learn to defeat an enemy that thrives in heat. Another could be Andu being from a hidden cold village and Naruto has to form an alliance with him to face a common threat.
One idea could be a story where a character has the power to control both fire and water, which is unheard of in the Fairy Tail world. This character could be an outcast at first but then becomes a key figure in a big battle against a powerful dark force.
One idea could be a character seeking revenge on a former friend who betrayed them. They plan their revenge carefully, using the other person's weaknesses against them.
One idea could be a story where one of the dalmatian puppies gets lost during a family outing and has to find its way back home, facing various challenges along the way.
One idea could be exploring the backstory of a minor character in the Bioshock universe. For example, a splicer's journey before they became spliced. It could show how they were once an ordinary citizen of Rapture and what led them to make the fateful decision to use ADAM. Another plot could focus on an alternate timeline where the protagonist makes different choices. Maybe they side with the wrong faction and have to deal with the consequences. A third idea is a story centered around a new type of plasmid that has unexpected effects on the user and how it impacts the power dynamics in Rapture.
Another plot could involve the creation of a female monster. In the original, Victor Frankenstein was hesitant to create a female. A fanfic could explore what would happen if he did. Maybe the two monsters would have a complex relationship, and together they would try to find a place in the world that would accept them.
One idea could be that Batman and Wonder Woman team up to stop an ancient, otherworldly threat that's beyond the capabilities of the Justice League alone. They have to travel to different dimensions and rely on each other's unique skills.