One plotline could be that they are in a dangerous situation together, and in a moment of relief after being saved, they share a spontaneous kiss. Another could be in an alternate universe where they are part of a different social structure and their relationship develops romantically over time, leading to a kiss. Maybe they are training together and a moment of intense emotion during training results in a kiss.
In many Naruto fanfictions, Sakura might be jealous of Hinata's relationship with Naruto. This could be because Sakura has her own unexpressed feelings for Naruto. For example, she may see Hinata's gentle and supportive nature towards Naruto and feel envious. It adds an interesting dynamic to the story as it can create tension between the characters.
One common theme is friendship - turned - love. They start as friends in the Naruto universe and then develop deeper feelings. Another theme could be mutual support. They both understand the challenges of being female ninjas, so they support each other in their growth.