Rather than seeking 'lemon' fanfiction which may not be in line with the general ethical and platform - allowed content, you could look for fanfictions that build on the unique bond between Kakashi and Naruko. For example, there might be stories about Naruko learning from Kakashi's experience, or Kakashi seeing Naruko as a symbol of hope in the new generation of ninjas. Check out the Naruto fanfiction sections on popular reading platforms.
I'm not sure specifically about 'kakashi and naruko lemon fanfiction' as 'lemon' often implies inappropriate content in fanfiction. However, there are many great Kakashi and Naruko fanfictions that focus on their relationship in a more positive and appropriate way, like those exploring their teamwork or how they grow together as comrades. You can try looking on well - known fanfiction websites like Archive of Our Own or FanFiction.net.
Most fanfiction platforms have strict rules against explicit or inappropriate content, so finding 'kakashi and naruko lemon fanfiction' might be difficult. But if you want to read about their relationship in a proper and interesting way, search for general Kakashi and Naruko fanfictions. These can include stories about their adventures together, or how they support each other during tough times in the Naruto universe.