Maybe the petting triggers a magical transformation for the fox or reveals a hidden power within it. This could take the story in a fantasy direction.
One possible storyline could be that Harry is cursed by a dark wizard. The curse has the unexpected side - effect of making him pregnant. He then has to search for a way to break the curse while dealing with the physical and emotional turmoil of pregnancy. Another could be that it's a result of some experimental magic gone wrong. He might have been trying to help someone with a fertility spell and it backfired on him.
One possible storyline could be about how Tsunade deals with the unexpected pregnancy in the context of her leadership role. She might have to balance her duties and the changes in her personal life.
One possible storyline could be the challenges Bella and Edward face as they prepare for a new life together while dealing with the vampire - human relationship issues. Maybe they struggle to keep Bella safe during her pregnancy considering her human frailty.
One possible storyline could be that Merlin makes a serious mistake in his magic that endangers Camelot, and as a form of punishment, he gets spanked. Another could be that he disobeys Arthur's direct order in a situation where it really matters, and this leads to the spanking as a disciplinary action. Maybe he accidentally reveals a secret that was crucial to keep, and the spanking is a way for the other characters to show their disappointment and enforce discipline.
One possible storyline could be that Tails gets involved in a dangerous adventure where he sacrifices himself to save his friends. For example, he might be facing a powerful new enemy that has invaded Sonic's world. Tails, being the intelligent and brave fox he is, uses his mechanical skills to create a diversion that allows Sonic and the others to escape, but in the process, he is fatally injured. Another storyline could be related to a disease outbreak in his world. Tails tries to find a cure but ends up being infected himself. As he weakens, he uses his last moments to pass on his research to the other characters so they can continue the fight. A third storyline could be a time - travel gone wrong. Tails might be sent to a different era where the conditions are too harsh for him to survive, and his death in that era has a profound impact on the future when Sonic and the gang discover what happened.
One possible storyline could be that they are in a committed relationship and the pregnancy is unexpected but they decide to face it together. They might struggle with how it will affect their hero careers and deal with the reactions of their friends and families.
One possible storyline could be that Brennan's friends and colleagues at the Jeffersonian are in a race against time to find the shooter while she is in critical condition in the hospital. They follow every lead, from her past cases to any personal enemies she might have made.
One possible storyline could be that Sirius initially panics when he finds out about the pregnancy. He might struggle with his responsibilities as he has a rather wild and carefree nature in the original story context. He could then gradually grow into the role of a father - to - be, facing challenges from his friends and family who may have different expectations.
Perhaps the fanfiction could focus on the wedding day itself. There could be a special arrangement to ensure that her epilepsy doesn't disrupt the ceremony. Her partner could have coordinated with the venue staff to have a quiet, safe space for her in case of a seizure. And the love and support from friends and family during the wedding would be a major part of the story.
One possible storyline could be that they face a lot of family drama. Their families might be shocked and have different reactions, some may be supportive while others are against it. It could also explore how Ben and Gwen deal with the sudden responsibility and how it changes their relationship from just being cousins to co - parents.