Perhaps the fanfic is set during a time when Korra has lost faith in herself. Tenzin, with his calm and collected demeanor, comforts her by sharing his own insecurities when he was young. He could tell her that everyone makes mistakes and that it's important to learn from them. This might lead to a series of training sessions where Tenzin not only trains Korra in airbending but also in building mental resilience, and their bond grows stronger through these shared experiences.
A common theme is the exploration of their age - gap relationship. Tenzin is much older, so there's often a focus on how they bridge that gap. Another theme is the clash between Tenzin's traditional airbending wisdom and Korra's more impulsive Avatar ways.
The cultural differences between the airbenders and Korra's background add depth. Tenzin represents the airbender culture with its focus on peace, detachment, and spiritual growth. Korra, on the other hand, comes from a more action - oriented background. In a comfort fanfic, these differences can be explored. For instance, Tenzin might introduce Korra to airbender meditation techniques to calm her down when she's stressed. The clash and then the harmony of these two cultures within the context of comfort make the fanfic an interesting read.
I'm not sure of specific Tenzin x Korra fanfic titles off the top of my head, but you can try searching on fanfiction.net as well. You might find stories that delve into their unique dynamic. Tenzin being an older and more experienced airbender and Korra as the young and headstrong Avatar could lead to some really interesting character - driven fanfic.
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.