One common theme is often the relationship between Isaac Clarke and the original character. It could be a romantic relationship that develops in the midst of the chaos of the Dead Space setting.
Survival is also a big theme. Given that the Dead Space universe is full of danger, the characters, including the original character, have to fight to survive. And within this context, their relationship with Isaac Clarke can grow and change. For example, they might rely on each other more as they face one threat after another. The 'lemon' aspect might be a way to show the deepening connection between them on an emotional and physical level in the face of such extreme circumstances.
Well, I'm not sure specifically which ones are the best. You could try searching on popular fanfiction websites like Archive of Our Own. They usually have a wide range of fanfictions related to Isaac Clarke and original characters. Just use their search function and type in 'isaac clarke oc lemon' to see what comes up.
Survival is a very common theme. Just like in the original Dead Space story, the female characters in these fanfics often have to fight for their lives in the face of the necromorphs. For example, in many of these stories, they are on a ship or station filled with danger and they have to use their wits and any available resources to stay alive.
One common theme could be adventure. Since 'the doctor' is often associated with traveling through time and space, the 'oc' can get involved in these exciting adventures. Another theme might be romance, as the relationship between the doctor and the oc is explored in different ways.
One common theme could be the power dynamic between the Joker and the OC. Since the Joker is such a complex and powerful character, exploring how an OC interacts with him in terms of power can be interesting.
Love and passion are very common themes. Since it's often about Damon, there's usually a strong sense of attraction and a complex relationship. For example, in many of these fanfictions, the OC might be initially hesitant about getting involved with Damon because of his reputation, but then they can't resist the pull towards each other.
Another theme could be self - discovery. The oc might be on a journey of self - discovery while being involved with Jasper. And the lemon elements can be seen as a part of that journey, a new experience that helps the oc understand themselves better in the context of the relationship. Also, power dynamics can be a theme, especially considering Jasper's character. The relationship might involve some give - and - take in terms of power, which is sometimes reflected in the lemon parts as well.
One common theme could be the exploration of Orochimaru's complex character in relation to the original character (OC). It might involve the OC being drawn into Orochimaru's world of dark magic and experiments. Another theme could be a relationship of power imbalance, where Orochimaru's power and influence play a major role in the story with the OC.
One common theme could be forbidden love. Since Loki is often portrayed as a complex and somewhat of an outcast character, a relationship with an original character in a 'lemon' context might involve a sense of secrecy or something that goes against the norms. Another theme could be power dynamics, where Loki's power plays a role in the relationship with the OC.
One common theme could be adventure. Since Ash is often associated with going on adventures in the Pokémon world, an original character might be added to his journey, and then a romantic or more intense relationship (the 'lemon' aspect) could develop during their travels.
Another theme might be self - discovery. As the characters interact in the fanfiction, they could be learning more about themselves. For paul and oc, this could be related to their individual personalities and how they change or grow through their relationship. For example, paul might discover a more tender side of himself because of oc, and oc might become more confident. It's all about how they evolve as characters within the story.