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.
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.
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 common theme is redemption. Karai often has a complex past, and in many fanfictions, Leonardo helps her find a path to redemption. Another theme is love and attraction. Despite their differences, they are often drawn to each other. For example, in some stories, their initial animosity turns into a deep - seated love over time.
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.
One idea could be that the little human sister discovers the Tmnt's lair by accident. Maybe she was exploring the sewers for a school project on urban infrastructure. Once there, she befriends the turtles and helps them out with some human - world tasks like getting supplies or finding information on their latest enemy.
One great tmnt human high school fanfiction is 'The Turtles in High School Chaos'. It has an interesting plot where the turtles try to blend in with human students while also dealing with their ninja duties.
One great 'human Leonardo and Karai fanfiction' is 'The Unlikely Bond'. It explores their relationship in a modern - day setting where they have to work together to solve a mystery in their city. It's really interesting as it shows their characters' growth and how they overcome their differences.
It often explores themes of family in a new way. Since she's their sister, it's not just about friendship or alliance. There's a sense of loyalty and protection that comes with the family bond. Also, the human sister can bring a different perspective to the turtles' battles and adventures, adding more depth to the story.
The unique part is often the blend of two different worlds. The turtles' ninja and mutant nature against the backdrop of a normal human high school. It's like seeing aliens in a regular school.