One common theme is the combination of different elemental powers. Since Naruto has his own set of abilities related to chakra and Korra is an Avatar with control over four elements, fanfics often explore how these powers can work together or create new forms of combat.
Another theme is the cultural exchange. Naruto comes from a ninja - based culture, while Korra is from a world with a more Asian - inspired Avatar - centric culture. Fanfics might show how they introduce their respective cultures to each other and how their friends and allies react to it. For example, Naruto might introduce his friends to the concept of the Avatar and Korra could show Naruto's gang some unique traditions from her world.
The theme of friendship and mentorship also pops up a lot. Given their different levels of experience (Naruto being very experienced by the end of his series and Korra being younger and still learning), fanfics may explore how Naruto can be a mentor to Korra, or how they can form a strong friendship based on mutual respect and learning from each other's strengths and weaknesses.
Chapter 311, "Expulsion and Unease, an Overzealous Xia Chuan (Part 3)", is the clearest early answer because it turns Yu Bin's situation into a concrete plot event. A useful checkpoint is the way the scene starts with On the contrary, Xia Chuan had several deep sword wounds on his... and follows through with They looked up at the killing intent on Xia Chuan's face, feeling a....
Chapter 348, "Schemes and Counter-Schemes, the Five of East Ridge, Zhu Yang's Threat, The Dust Settles (Part 6)", is the clearest early answer because it turns Zhu Yang's situation into a concrete plot event. The setup is Lu Yang thought of something and laughed, "Besides, I remember that..., but the pressure keeps building through In the second year of Great Xia in the Logging Realm, they were....
Chapter 339, "The Changes of Li Hu and Yang Zhong, the Hou Family's Opportunity, Advice (Part 5)", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. It opens with The Lingbei, Longshan, and Beehive factions in Xia City have long... and closes on Hou Bing was slightly stunned and asked in confusion: "Isn't it just....
Chapter 350, "Pathways to Promote the Peak of Cold Resistance, Moao's 10th Town, Beishuo's Yang Fa, Nightmare, East Ridge's Lu Yun", is the clearest early answer because it turns Lu Yun's situation into a concrete plot event. Early on, Xia Hong took a deep breath, looking at the sky already showing a.... By the end, Zhu Baixu was about to continue questioning, but Lu Yun spoke first,....
Chapter 341, "Moao's Nine Garrisons, the Inspection System and Zhenyu, Li Hu and Hong Yuru (Part 4)", is the clearest early answer because it turns Zhu Tong's situation into a concrete plot event. The setup is After explaining the general situation he had seen, Lu Yang's brows..., but the pressure keeps building through Every figure is very vague, making it obviously difficult to report....
Chapter 267, "Betting Agreement", is the clearest early answer because a shaky connection becomes usable in the plot. A useful checkpoint is the way the scene starts with Jiang Li had just turned around when she was suddenly embraced by a...
Chapter 287, "Cloud Dragon Army's First Battle, Zhou Yuan's Bloody Struggle, Decisive Victory and Unexpected Windfall (Part 3)", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter gives readers a real answer by opening on The problem is, they still can't make any counterattacks. and ending on The banner flapped wildly in the battlefield wind, and the Cloud Jiao....
Chapter 23, "Became Trending for Being Scolded", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event. The chapter turns that into something concrete by moving from Although Jiang Li exerted very little strength, Jiang Yan instantly...
Chapter 301, "Long Mountain Marches In, Defying the Enemy to the Death", is the clearest early answer because the violence around Great Xia becomes final instead of hypothetical. The chapter turns that into something concrete by moving from Seeing the actions of the Xia Army, Li Xuanling was not only... to Under the pressure of the massive number of Cold Resistance Level,....
Chapter 309, "Gamblers at the End of the Road, Li Family's Swan Song", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. Early on, The disciples of the Li Family, upon hearing these words, immediately.... By the end, Why would they risk everything to gamble with you?" Li Xuanping,....