I'm not sure specifically as there could be many novels with this title or concept. It might be about strong female characters (alpha females) and the idea of karma, perhaps how their actions, good or bad, come back to them in some way.
Yes, there are quite a few. Some focus on their unique relationship dynamics within the omegaverse setting. For example, there are stories that explore how Karma, as an alpha, protects Nagisa, the omega. They often involve elements of trust and growth between the two characters.
You can try Archive of Our Own (AO3). It has a large collection of fanfiction, and there are likely many works related to this pairing. Just use the search function and type in 'alpha karma x omega nagisa' to find relevant stories.
Strange Tales from a Chinese Studio is an ancient Chinese novel. It tells many fantastic stories, including many plots about karma. In these stories, people could often see the scene of good and evil being rewarded, and the retribution of good and evil was sometimes beyond people's imagination. For example, in the Legend of the White Snake, the White Lady sacrificed everything to save her husband Xu Xian, but in the end, she was punished by the heavens and lost her beauty and life. The power of karma made people feel deep fear and vigilance in the story.
One possible fanfiction could be about female Karma's journey in the Assassination Classroom. Maybe she uses her intelligence and unique skills to outwit the other students in various assassination attempts. For example, she could come up with creative plans to get close to Koro - sensei while still maintaining her cool and mysterious demeanor.
She could have a secret power that only she discovers over time. For instance, the power to read Koro - sensei's thoughts briefly when she makes direct eye contact with him. This would give her an edge in the assassination attempts. She could then use this power to set up elaborate traps based on what she learns from his thoughts.
Alpha females are usually highly ambitious. They strive for success in their careers or personal goals. They might set high targets for themselves, like aiming to become the top executive in a company within a few years.
If it was a positive relationship, God would use a series of hints and reminders to make you realize the uniqueness of this relationship. These hints might include the feeling of rapid heartbeat, similar values and goals, and deep spiritual communication. When you meet someone who makes your heart beat faster, this might be one of the obvious signs of good karma. In addition, when two people start to get along, they will find that they have similar values and goals, which allows them to support and encourage each other in the face of difficulties and challenges. True love was built on deep spiritual communication. If you could have deep spiritual communication with the other party, this was also one of the manifestations of positive fate. In short, if it was a good relationship, God would use these hints and reminders to let you feel the special power of this relationship.
One common theme is friendship development. Since they have an interesting dynamic in the original work, in fanfictions, it's often explored further as they face new challenges together. For example, they might have to work together to solve a mystery in the school.