The theme of friendship and mentorship also pops up a lot. Even though they are from different eras, they can still form a bond. Aang can act as a mentor to Korra, guiding her through spiritual challenges that he has already faced. And Korra can show Aang how the world has changed and how she is adapting to new threats in a different time.
One great aang and korra fanfiction is 'The Avatar's Bond'. It beautifully explores the relationship between Aang and Korra across different timelines. They face challenges together and learn from each other's experiences as Avatars.
Well, perhaps Korra could learn some of Aang's early airbending techniques. Since Aang was the first Avatar to master airbending in a long time, he might have some unique knowledge to share.
The Legend of Korra comics are definitely worth a read. They capture the essence of the franchise and bring fresh perspectives. The quality of the storytelling and the visuals make them a great addition to the series.
The 'lemon' aspect might be a bit hard to come by in a clean way as it often involves inappropriate content. But for normal Korra and Mako fanfictions, you could also try FanFiction.net. Some stories there might show their relationship developing, their adventures together, and how they support each other, which can be really interesting to read.