They might develop a mentor - mentee relationship. If Craig is more experienced in the ways of the world outside the barbarian tribes, he could mentor Tweek on how to navigate different cultures and situations. Tweek, on the other hand, could be Craig's mentee in terms of physical strength and combat skills, which could come in handy for Craig when he gets into trouble.
One plot idea could be that Tweek, the barbarian, is on a quest and stumbles upon Craig, the thief, who has stolen a valuable artifact. Tweek initially wants to take the artifact from Craig for his own tribe but as they interact, they realize they need to work together to keep it out of the hands of a more malevolent force. Maybe they start to develop a friendship or even something more along the way as they face various challenges.
Show their relationship evolving through helping each other out in difficult situations. For example, if Jason gets injured while exploring a dangerous part of the Creek, Craig could be the one to take care of him and help him get back to safety. This act of kindness can make Jason see Craig in a new light, and vice versa. Then, they can start to become closer friends, sharing secrets and having inside jokes that are unique to their relationship.
In a fanfiction, their relationship might start off rocky. Deadpool's crazy antics would likely put Peter off at first. But as they face challenges together, they could grow to respect each other. Deadpool might learn some sense of responsibility from Peter, and Peter could loosen up a bit thanks to Deadpool's carefree attitude. Eventually, they could become a great superhero duo, with Deadpool providing the comedic relief and Peter the moral compass.
Another common theme is adventure. Writers like to take the two characters on different adventures in South Park or even outside the town. It adds an element of excitement and exploration to the stories.
A mentor - mentee relationship could develop. The Winchesters, with their years of experience in fighting all kinds of supernatural beings, could mentor Harry. They could give him tips on combat strategies, survival skills, etc. Harry, on the other hand, could learn a great deal from them and maybe even apply some of those skills in his own world.
They could develop a mentorship - like relationship. Lois, with her knowledge of the superhero world and her experience in dealing with complex personalities, could guide Conner. He, in turn, could offer her a fresh perspective on the world of superpowers.
They could develop a mentor - mentee relationship. The future Tsuna has more experience and knowledge, so he can guide the present Tsuna.
They might develop a friendship. Harry could see Daphne's kindness beneath her Slytherin exterior at the Yule Ball, and Daphne could realize that Harry is not just the 'Chosen One' but also a normal boy with normal feelings. This new understanding could lead to a friendship where they support each other through the challenges at Hogwarts.
Another theme is likely the relationship development between Craig and Tweek. The pregnancy can be a catalyst for them to grow closer or face new challenges in their relationship. They might have to deal with things like responsibilities, future plans, and changes in their dynamic. It could also explore how they handle the stress and emotions that come with an unexpected pregnancy.
Well, one aspect could be the exploration of possessive behavior in relationships. In a Craig x Tweek fanfiction, Craig's possessiveness might add an interesting dynamic. It could show his intense feelings for Tweek, perhaps born out of a fear of losing him. Maybe in the story, this possessiveness causes some conflict, like Tweek feeling smothered at times but also realizing it's a sign of Craig's deep love for him.