Sakura would probably be very hurt at first. She might cry a lot and feel betrayed. But then, she'd likely draw on her inner strength. She is a strong - willed character after all. She could focus on her work as a medical ninja to distract herself from the pain. And she would also have her friends to turn to for support, like Naruto who has always been there for her.
Another reaction could be that Sakura tries to follow Sasuke. She believes that she can change his mind or that she can be of help to him. She might leave her own responsibilities behind for a while to chase after him, thinking that their bond is strong enough to overcome whatever is making Sasuke leave.
In such a fanfic, it might explore the challenges they face. For example, Sasuke's past actions might make some in the village still be wary of him. But Sakura's pregnancy could be a symbol of hope and new beginnings. It could also show how their friends like Naruto react to the news. Naruto, being Sasuke's long - time friend, would likely be overjoyed and offer his support, while also teasing Sasuke about becoming a dad.
One possible plot could be that Sasuke leaves Sakura to pursue a solo mission of redemption. He feels that his past actions have left a stain on his honor and he must atone for them alone, believing that being with Sakura would only hold him back from his self - imposed penance.
There are quite a few fanfics out there. One I remember has Sakura's growth as a ninja intertwined with her feelings for Sasuke. It shows how her experiences, like dealing with the fall of Sakura leaves in the village, symbolize her changing relationship with Sasuke. Another one focuses on Sasuke's return to the village and how Sakura, with the reminder of the sakura leaves (a symbol of new beginnings in their village), tries to reconnect with him on a deeper level.
One common theme is the exploration of unrequited love. Sakura's love for Sasuke is well - known, and when he leaves her for Karin, it delves into the pain of unrequited love from Sakura's perspective. Another theme is the idea of choosing based on power and usefulness. As Karin has certain powers that can be of help to Sasuke, it shows a theme of practicality in relationships.
Naruto might initially be in denial. He's so used to having Sakura around and believing that they have a future together. So when she leaves for Sasuke, he might think it's just a temporary thing or that she's been influenced by something or someone. But as time passes and he realizes it's real, he would be deeply hurt. He might also start to question his own self - worth, thinking that he wasn't good enough for Sakura. And he might even try to win her back at first, but then slowly come to accept the situation and focus on his other responsibilities like being a ninja and protecting the village.
Another great one is 'Pregnancy and Promise'. This fanfic emphasizes the promises Sasuke makes to Sakura and their unborn child. It shows the emotional turmoil and the hope that comes with the pregnancy in their relationship.
In some fanfictions, Sakura may be determined to find Sasuke and bring him back. She could set out on her own journey, facing various challenges along the way, and growing both as a person and as a ninja in the process of trying to reunite with him.
There are fanfics like that. Sasuke might leave Sakura for Karin because of Karin's loyalty. Karin has shown unwavering loyalty to Sasuke throughout the series. She was willing to risk her life for him on multiple occasions. In contrast, Sasuke might think that Sakura's love is more of a childhood crush that she hasn't fully grown out of, and he may be drawn to Karin's more mature and selfless loyalty.