There are several common themes. For instance, the theme of forbidden love. Given their different allegiances in the Overwatch universe, their relationship might be seen as something that's not supposed to happen. This can add a lot of tension to the story. Another theme is the power dynamic between them. Sombra has her hacking abilities and Bridgette her combat skills, and fanfictions might play with who has the upper hand in different situations, and how that affects their relationship.
A frequent theme is the exploration of their different backgrounds. Sombra coming from a more shadowy, underworld - like background and Bridgette from a more traditional hero - making place. Their relationship in fanfiction might be about bridging those two worlds. Also, trust is a big theme. Since Sombra has a reputation for being sneaky, stories often revolve around whether Bridgette can trust her and how that trust develops or breaks down.
One common theme is the overcoming of differences. Since they might have different personalities, fanfictions often explore how they deal with that. Another could be adventure. They might go on some sort of journey together.
Another theme could be adventure. If they are from a universe where there are exciting events or quests, the fanfiction might focus on them going on an adventure together, which in turn strengthens their bond. For example, they might have to solve a mystery or defeat a common enemy. And during this process, their relationship deepens.
One common theme is the idea of a secret relationship. Since both characters have rather mysterious and shadowy aspects to their personalities in the game, it makes sense that their relationship in fanfiction would often be hidden from others. For example, they might meet in secret locations within the Overwatch universe.
One common theme could be friendship development. Maybe they start as acquaintances and gradually become really close friends, sharing secrets and having adventures together.
Another theme is the discovery of self - worth. Sombra might start to see her value differently when she's around the Radiant. For example, in some stories, she realizes she can use her skills for good instead of just her own gain. This theme is explored through her interactions with the Radiant members.
A common theme is the exploration of their individual insecurities within the context of their relationship. Soldier 76 may be insecure about his past actions and how they are perceived, while Sombra may be insecure about her place in the world. Their relationship in the fanfiction can be a way for them to overcome these insecurities. Also, the theme of sacrifice often comes up. They might be put in situations where they have to sacrifice something for the sake of the other or for the greater good, which adds depth to their relationship.
One common theme is the idea of redemption. Sombra, often seen as a more morally ambiguous character, may find redemption through her relationship with the more heroic Tracer. Another theme is trust. Since they are from different backgrounds, building trust between them is often explored. For example, in many fanfictions, Sombra has to prove herself to Tracer.
Another theme is the idea of redemption or change. Sombra might be seen as a character who could help Symmetra break out of her very strict ways, or Symmetra could be the one to make Sombra more responsible. It's about how they influence each other's growth.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3). There are often a plethora of fanfictions about various pairings, including Sombra x Bridgette. Another option is FanFiction.net, though the tagging system might require a bit more searching. You could also check out Tumblr, as many fans share their fanfiction there or link to other sources.
Well, themes like forbidden love are quite common. Since King Sombra may be an 'outsider' or a 'bad guy' in the original context, a relationship with an OC can be seen as something not allowed. Also, themes of discovery are there. The OC might discover secrets about King Sombra or vice versa, which drives the story forward. And then there's the theme of transformation, where either the OC or King Sombra changes because of their interaction.