In Sasuke and Sakura birthday lemon fanfictions, a major aspect is the use of the birthday as a catalyst for character development. For Sasuke, it could be a time when he realizes how much Sakura means to him and starts to let go of some of his past traumas. Sakura, on the other hand, might see Sasuke's birthday as an opportunity to show him that he is loved and supported. The 'lemon' aspect, if it's not too adult - oriented, could be some sweet, romantic and slightly spicy moments between them, like a passionate kiss under the stars on their birthdays or a warm embrace that holds a lot of unspoken feelings.
Well, in these fanfictions, the setting is important. Since it's for their birthdays, it could be a beautifully decorated place like a garden full of cherry blossoms for Sakura or a more private, serene location for Sasuke. Their character traits play a big role too. Sasuke might show a softer side on his birthday, and Sakura's determination to make the day great for him would be highlighted. And of course, there could be some cute moments like Sakura baking a special cake for Sasuke, which shows her love and care in a very domestic way.