The OC should have a clear motivation that ties into Tai Lung's world. For example, if the OC is also a martial artist, they could be seeking to prove themselves against Tai Lung, which immediately creates a connection.
One type of Tai Lung fanfic could be a 'what - if' scenario. What if Tai Lung had been redeemed? Writers could create a story where he overcomes his pride and anger, and uses his skills for good. This would change the whole dynamic of the story and give a new perspective on his character.
Often in fanfiction, Tai Lung's split between good and evil is a central theme. His upbringing in the kung fu temple might have instilled certain values that are considered 'good', like discipline and respect for the art. However, his jealousy towards Po and the sense of being wronged when he was denied the Dragon Scroll could be seen as the catalysts for his 'evil' transformation. Authors might explore how he could have been redeemed if he had been able to balance these two sides of his nature, or how his 'evil' side completely took over due to the circumstances.
Tai Lung fanfic often gives readers a chance to see the character in a new light. It can show his softer side, which was not much explored in the original. Maybe he has a love interest that no one knew about, and a fanfic can build a whole story around that relationship.
First, understand the characters well. Tai Lung is a complex character, driven by his ambition and his sense of being wronged. Tigress is strong - willed and dedicated to her training. Start with a strong concept, like how their two different worlds collide. For example, if Tai Lung returns seeking revenge but Tigress tries to reason with him. Then, build the tension gradually. Don't rush their relationship. Let them have exchanges, both physical in fights and verbal in arguments and conversations.
Their relationship might develop through shared combat experiences. For example, they could be forced to team up against a new, powerful enemy. During the battles, they see each other's strengths and weaknesses and start to respect one another, which could be the start of their love story.
In a fanfic, Tai Lung could be redeemed. Maybe he was wrongly influenced in the past. Po, being the kind - hearted panda, decides to help Tai Lung find his true self. They start training together, and Tai Lung begins to see the value in the Dragon Warrior's way of life. Their relationship evolves from enemies to something more like mentor - mentee in a reversed way, with Po guiding Tai Lung.
Another storyline might involve a time - travel element. Tai Lung and Tigress are sent back in time to when Tai Lung was still a young student. Tigress, knowing what will happen in the future, tries to steer Tai Lung away from the path of jealousy and anger. They could form a bond as friends and training partners, and this new relationship changes the course of events, preventing Tai Lung's fall from grace.
One common theme could be the exploration of their relationship in a more romantic or complex way. Since they are from different sides in the Kung Fu Panda universe, there might be themes of redemption and understanding in the fanfiction.
For Tai Lung, in fanfictions, his character could be developed by exploring his backstory more deeply. Maybe there were events in his childhood that made him so desperate for the Dragon Scroll. This could make readers sympathize with him more. Tigress could be developed in terms of her relationships with other characters. For example, how her relationship with Tai Lung affects her relationship with the Furious Five. She might become more independent from the group as she spends more time with Tai Lung. And Tai Lung could be developed to be more adaptable. He could learn new ways of thinking and being from Tigress, and Tigress could learn to be more assertive from Tai Lung's boldness.