For Tomoyo, she might be overjoyed as she has always been supportive of their relationship. She could see this kiss as a sign of their relationship deepening and might start planning more things for them, like new outfits for their future 'dates' in card - capturing adventures.
A fanfiction could focus on Sakura and Syaoran's daily life after the main events of Cardcaptor Sakura. Maybe they are training new cardcaptors. They could be facing challenges like how to teach the newbies about the importance of the cards and the right way to use their magic, all while their relationship continues to develop in this new phase of their lives.
A pregnancy would likely strengthen their relationship. They would become more reliant on each other, sharing the joys and fears of impending parenthood.
Perhaps it's a goodbye kiss. Syaoran has to leave for a while, and in a very emotional moment, they kiss. It shows their deep love for each other and the pain of separation. In the fanfiction, this could lead to a series of events where Sakura is constantly longing for his return.
Adventure is also quite common. Fans like to write about Syaoran going on different adventures, either related to collecting cards or something completely new. Growth as a character is another theme. Fanfictions often show Syaoran growing, becoming more powerful, and maturing both in his magic skills and in his relationships.
At first, Syaoran is rather cold and competitive towards Sakura. But as they go through various card - capturing adventures together, he starts to see her in a different light. His feelings gradually change from rivalry to admiration and then love.
Their relationship would become more domestic. They would have to rely on each other more for daily things. For instance, Syaoran might cook breakfast for Sakura on some days, and Sakura would do the laundry. They would also be more open with their feelings, not holding back like when they were just dating.
Regarding the relationship with other characters, Kakashi's overprotectiveness of Sakura can strain relationships. For example, the other ninja in the village may think Kakashi is playing favorites, which could lead to resentment among some. With their own teammates, it can be a bit of a mess. Naruto might try to understand at first but as time goes on, he may get frustrated that Kakashi seems to be only concerned with Sakura's safety. Sasuke may view it as a sign that Sakura is not as strong as she claims and this could further damage their already complex relationship.
Love is a very common theme. Since they have a special connection in the original series, fanfictions often explore the growth of their love. Another theme is adventure. They are both involved in magic, so new adventures are often written about. For example, they might go on a quest to find a lost Clow Card.
One interesting fanfiction could be about Sakura and Syaoran going on a new adventure together in a parallel world. They might face new Clow Cards or some other magical threats. In this story, their relationship could grow even deeper as they rely on each other to overcome difficulties.
It deepens their relationship. A kiss is a very intimate act. For Naruto and Sakura, it could be the start of a more romantic relationship. It might make them more aware of each other's feelings and lead to them spending more time together, getting to know each other on a different level than just friends or comrades.