Perhaps a fan fiction where Tigerclaw gets injured and Leonardo has to decide whether to save him or leave him. This moral dilemma could explore Leonardo's character. If he saves Tigerclaw, it could lead to an unexpected alliance or at least a truce between them, with Tigerclaw having a change of heart due to Leonardo's mercy.
One idea could be a story where Leonardo and Tigerclaw are forced to team up temporarily to defeat a common enemy greater than their rivalry. Maybe a new, powerful mutant emerges that threatens both the turtles and Shredder's plans. This would put them in a situation where they have to rely on each other's skills.
A plot could revolve around Leonardo trying to understand Tigerclaw's motives more deeply. He might discover that Tigerclaw wasn't always the villain he seems to be. For example, there could be flashbacks to Tigerclaw's past, showing how he came to be under Shredder's control, and Leonardo could try to use this knowledge to turn Tigerclaw away from his evil ways.
Leonardo would be a likely candidate. He is often the most level - headed of the turtles and believes in honor and justice. He might see the potential for a greater good if he can end the hostilities with Tigerclaw, so he could be the one to make the first move towards a truce.
The conflict between good and evil is a key element. Leonardo represents the good, and Tigerclaw is clearly on the side of evil. Their clashes, both physical and ideological, can create a lot of tension and excitement. For instance, their different fighting styles - Leonardo's ninjutsu training with Splinter versus Tigerclaw's more brute - force and underhanded tactics. Another element is the mystery around Tigerclaw. There could be parts of his past that are slowly revealed in the fanfiction, which could add depth to the story.
One possible storyline could be a battle of wits between Leonardo and Tigerclaw. Leonardo, being the leader of the Turtles, would constantly try to outsmart Tigerclaw. For example, he could set up elaborate traps to catch Tigerclaw and stop his evil plans. Tigerclaw, on the other hand, would be constantly trying to anticipate Leonardo's moves and turn them against him. Another storyline could be a more complex relationship where they start to understand each other's motives over time. Maybe there could be a situation where they have to team up against a common, even greater enemy. This could lead to a begrudging respect between them.
Maybe in the fanfiction, there is a prophecy that involves Tigerclaw and Leo. They are initially skeptical but as strange events start to unfold around them, they are forced to work together. Along the way, they face many challenges like distrust from their own sides, but their growing friendship helps them overcome all that.
Maybe in a different universe where their clans have a more peaceful co - existence. Leonardo and Karai meet during a cultural exchange of sorts between the turtles and the Foot Clan. As they learn about each other's cultures and values, they grow closer.
Another interesting plot could be that the reader is a time - traveler from the future. They come back to the present day and meet Leo. Leo is initially suspicious but as they work together to prevent a future disaster that the reader knows about, they fall in love. It adds an element of mystery and adventure to the story. Plus, the time - travel aspect can bring in different versions of the TMNT universe and how they interact with the current situation.
One plot idea could be that Leonardo and White get involved in a mystery together within the Kekkai Sensen world. They might have to uncover a secret organization's plot that endangers the city. Another could be a story where they go on a journey to find a lost artifact that has special powers related to their world. Maybe they start off not getting along but as they face challenges, they grow closer.
A possible plot for the leonardo and karai lemon fanfiction could be that there is a prophecy about their union being the key to saving their world. At first, they are reluctant and even hostile towards each other. But as they start to explore the prophecy and what it means, they begin to develop feelings. Along the way, they have to overcome the distrust of their respective groups, and their relationship blossoms as they fight for the greater good.
Perhaps a plot where the gender - bent Leonardo is the only female in a group of male characters, and there are some romantic sub - plots that develop because of this dynamic. For example, she might have a love - hate relationship with one of the male characters which adds an interesting layer to the story. Another idea could be that she discovers a new power or ability that is related to her being female, which was not present in the original male Leonardo's story.
One idea could be that the Turtles from 2003 get transported to the 2012 universe and they have to deal with the different versions of their enemies. For example, the Shredder in the 2012 version might have some new powers or tactics that the 2003 Turtles aren't used to.