It can start with mutual distrust. Doomguy is used to killing demons, and the female demon is afraid of him. But when they are forced into a situation where they have to rely on each other to survive, like being trapped in a small area surrounded by more powerful demons, they start to see each other in a new light. They begin to communicate, first out of necessity, and then gradually become more open with each other.
A prevalent theme is the oc bringing a different perspective to the Doom world. Since the Doom universe is so dark and violent, the oc can be a source of light or hope. For example, the oc might have special powers or knowledge that helps Doomguy in unexpected ways. Also, the theme of redemption can be present if the oc has a troubled past and Doomguy's actions inspire them to become a better person. In some fanfictions, they might also face challenges together that test their relationship, like dealing with a powerful new demon threat or a moral dilemma within the Doom setting.
The relationship could develop through shared dreams. Isabelle and the human start having the same strange dreams every night. At first, they are confused, but as they start to communicate about these dreams, they find a deep connection. This unique way of communication could be the starting point of a very special relationship.
One common theme is the combination of their combat styles. Doomguy is known for his brutal and high - tech combat against demons, while Goblin Slayer uses more traditional and strategic methods against goblins. Fanfics might explore how they would team up in battles and what new tactics they could come up with.
A common trope is the 'enemies to lovers' or at least 'rivals to lovers'. Since they have different personalities and ways of doing things in the Shadowhunter world, it can be interesting to see how they overcome their differences. Another is the 'hurt/comfort' trope, where one of them gets injured or is in a difficult situation and the other provides support and care.
Doomguy is a very silent and rage - filled character. He just wants to kill demons. Goblin Slayer is more focused on goblins specifically. Their personalities might clash at first because Doomguy might see goblins as too easy of a target compared to demons. But they could blend as they both have a single - minded determination in combat.
Sure. You can check out websites like Archive of Our Own (AO3). Just search for 'doomguy x oc' there and you'll find a variety of fanfictions. Some might focus on their adventures together in the Doom universe, while others could explore a more romantic side of their relationship.
A possible plot is that the female demon is a half - demon, half - something else (like an angel perhaps). Doomguy is intrigued by her dual nature. As they team up, she tries to resist her demonic instincts while Doomguy tries to trust her. Their relationship could be full of tension as they both struggle with their own natures and the outside forces that want to keep them apart.
Romance is also quite prevalent. Writers might explore the relationship between Isabelle and the wolf, how they fall in love, overcome differences, and build a relationship. There could be cute moments of flirting and getting to know each other.
I'm not sure which specific 'Mayor X Isabelle' fanfiction is available. You could try searching on fanfiction websites like Archive of Our Own or FanFiction.net. They usually have a wide variety of fan - created stories.