Well, a major theme is growth. Both Zuko and the OC usually experience personal growth. For Zuko, it could be growing as a leader, and for the OC, it could be growing in confidence or in their abilities. Cultural differences are also common. Since the OC is often an original creation, there can be interesting interactions between their culture (if any) and the Fire Nation culture. And of course, friendship is a theme. Sometimes the relationship between Zuko and the OC starts as a friendship and then may or may not develop into something more romantic.
A descendant of a long - forgotten fire - bending clan that was known for their black fire abilities could be the main character. This character might have grown up not knowing about their special heritage until certain events unfold that awaken their black fire powers.
One idea could be exploring the origin of the black fire in the 'Legend of Korra' universe. Maybe it was a long - lost form of bending that was once used for evil but could be redeemed. Another could be a story where a new character discovers they have the ability to control black fire and must learn to master it while facing discrimination from other benders.
Sure. One great 'Fire Lord Zuko and OC fanfiction' is 'The Fire Within Her'. It has an interesting plot where the OC is a powerful water bender who crosses paths with Zuko. Another is 'Zuko's Unlikely Ally' which shows a really unique relationship develop between Zuko and the OC as they face various challenges in the Fire Nation. There's also 'A New Beginning with Zuko' that focuses on how the OC helps Zuko rebuild the Fire Nation in a more positive way.
One great korra x zuko fanfic is 'The Fire and the Water'. It beautifully weaves their different personalities and abilities together. The story takes place in a post - war world where they have to work together to rebuild. Another is 'A New Alliance' which focuses on their growing friendship that slowly turns into something more. It has really interesting dialogue that makes you feel like you're right there with them.
The contrast between their characters. Korra is brash and bold, while Zuko has a more complex and brooding personality. When these two are paired in a fanfic, it creates a lot of interesting dynamics. Their different bending abilities also add to the allure. Fire and water, which are opposing elements, can represent their relationship in many ways.