Yes, there are likely some popular ones. Often, these fanfictions gain popularity because they explore the relationship between Mako and Korra in a way that the original show might not have fully delved into. For example, some might focus on the emotional build - up to the kiss, which can be really engaging for fans who are invested in their relationship.
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.
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.
Ichigo's Soul Reaper powers are based on spiritual energy, and Korra's bending is based on her connection to the elements. Their powers could interact in a way that creates a new form of energy. For example, when Ichigo uses his Getsuga Tenshou near Korra while she's bending, it might create a shockwave that combines the force of the spiritual energy blast with the element she's bending. This could be a very powerful and unique combination that they could use to defeat enemies.