Love and friendship are also big themes. The OC and Sirius usually start as friends or strangers and then develop a deep romantic relationship. Their love story might be set against the backdrop of the wizarding world's turmoil, like the fight against Voldemort. It adds an element of danger and excitement to their relationship.
Another theme is discovery. The OC, being an original character, is often in the process of discovering the wizarding world, and Sirius, with his knowledge and experience, helps her. At the same time, Sirius might also be rediscovering himself through his relationship with the OC. This mutual discovery creates interesting storylines and character development.
One common theme is forbidden love. Since Sirius has his own complex situation within the wizarding world, often the relationship with the OC is something that is not easily accepted. For example, in many stories, his family might oppose it.
Love and friendship are also common themes. The OC often forms a deep bond with Sirius, whether it's a romantic love or a strong friendship. This bond helps to develop both characters and drive the story forward. They might go through challenges together and their relationship grows stronger as a result.
Another theme is the growth of the relationship. The pregnancy can either strengthen or test the bond between Sirius and the OC. Sometimes it shows how they come closer together, learning about each other on a deeper level.
One common theme is redemption. Often, Sirius has had a rough past, and the OC can play a role in his redemption. For example, in some fanfictions, the OC helps Sirius come to terms with his family issues and his time in Azkaban. Another theme is love and acceptance. The OC may be an outcast in some way, and Sirius and the OC find solace in each other's company, accepting each other's flaws.
Love is a very common theme. The love that develops between Sirius Black and the OC can range from a slow - burning romance to an instant attraction. Another common theme is redemption. Sirius may find redemption through his relationship with the OC.
Love and Romance are very common. Since it's about Sirius Black and an OC, the development of their relationship, from the first meeting to falling in love, is often a central theme.
The theme of freedom is quite important too. Sirius was locked up in Azkaban for a long time, and when he escaped, he was fighting for his freedom. Fanfictions often expand on this, showing his journey to fully regain his freedom and his place in the wizarding world, while also dealing with the prejudice against him because of his supposed crimes.
The theme of redemption also shows up. Since Sirius had a somewhat 'tainted' reputation in the eyes of the Black family, some fanfictions explore if Orion could have played a role in his redemption or if Sirius could have redeemed the family name in Orion's eyes.
One common theme is the vulnerability of Sirius. Usually, he's portrayed as this strong, brave character, but when sick, he shows a different side. Another theme is the support from his friends and family. They often rally around him, highlighting the importance of those relationships.
One common theme is family conflict. Sirius rebels against the pure - blood mania and dark magic - associated ways of the Black family that Walburga represents. Another theme is the struggle for identity. Sirius is trying to be his own person away from the expectations set by his family with Walburga as a symbol of those family constraints.