A possible plot could be that they get married in a hurry due to some external threat. Like a new powerful enemy appears who has a vendetta against the Tendo family and Ranma's marriage to Shampoo could somehow be a way to unite forces and fight back. Or, perhaps they decide to get married secretly at first, but then they have to deal with the reactions of their friends and families when the news gets out. Also, there could be a plot where Shampoo's village has some sort of prophecy about her marriage to Ranma and they have to fulfill certain tasks according to the prophecy to ensure a happy married life.
One interesting plot idea could be that they have to overcome cultural differences. Shampoo is from a different background with her own traditions. For example, her family might have certain expectations for the wedding that Ranma and his family find strange. Another idea is that they face competition from other characters who are jealous. Maybe Ukyo doesn't want Ranma to marry Shampoo and tries to interfere. A third plot idea could be that they have to deal with Ranma's curse in a new way during their married life. Maybe Shampoo discovers a new method to control it that has never been thought of before.
One idea could be that they have to deal with the challenges of impending parenthood while still having their usual identity - switching mishaps. For example, Ranma might switch into his female form at an inconvenient time during the pregnancy, causing all sorts of comical and yet heart - warming situations as they figure out how to handle it together. Another plot could be that Ryoga discovers a new sense of responsibility and tries to build a proper home for their future family, all while Ranma is dealing with the physical and emotional changes of pregnancy.
One idea could be that Girl Ranma and Ryoga are forced to team up for a school project. They initially bicker a lot, but as they work together, they start to understand each other better. For example, Ranma might learn about Ryoga's insecurities when it comes to his sense of direction, and Ryoga could see that Ranma is not as tough as she seems on the outside.
In a 'Shampoo pregnant Ranma' fanfic, perhaps Shampoo gets pregnant by accident. This could lead to a lot of drama. Akane might be jealous or confused. Shampoo's family might have their own expectations and traditions regarding pregnancy. Ranma would be in the middle, trying to balance his relationship with Shampoo, his friendship with Akane, and the whole situation with Shampoo's pregnancy. There could be a journey of self - discovery for both Shampoo and Ranma as they face this unexpected event in their lives.
One popular theme is their martial arts adventures. They could be on a quest to find a new martial arts technique together. Another theme is their relationship development in a more platonic or romantic - but - clean way. For example, how they slowly understand each other's feelings through daily interactions.
One popular theme is the exploration of their complex relationship. Shampoo's love for Ranma and Ranma's often confused feelings towards her make for interesting character dynamics. Another theme could be adventure, as they often get into various misadventures in the original series, and fanfiction might expand on those. Also, cultural differences between them, since Shampoo has her own unique Amazon culture, can be a theme where fanfiction delves into how that affects their relationship.
Another plot could involve them having to deal with family drama before the wedding. Maybe Ranma's father has some outlandish requests or Akane's family has some concerns. But through it all, their love for each other prevails and they finally tie the knot in a beautiful ceremony by a cherry blossom tree.
One plot idea could be Ranma getting transported to the Fairy Tail world and having to learn magic. Another is a team - up where the characters from both series face a common enemy. Maybe a dark magic user who wants to use Ranma's unique curse for their own evil purposes.
Well, a cool plot for Percy Jackson and Ranma fanfiction could be that the gods in Percy's world get curious about Ranma's unique curse and decide to bring him to Camp Half - Blood. There, Ranma has to learn to co - exist with demigods while also trying to find a way to break his curse. Or perhaps there's a prophecy that only Percy and Ranma together can fulfill, which forces them to team up and journey across different realms.
One idea could be that Ranma somehow gets transported to the DBZ universe. He could end up training with Goku and learn the Kamehameha wave, but with his own Ranma - style twist. Maybe he uses his martial arts skills from his world to create a new fighting style combined with ki. Another plot could involve the Dragon Balls. Ranma might accidentally make a wish on them that gets him involved in a big battle against a powerful villain in the DBZ world.
One idea could be Ranma exploring different sports while staying female. Since she has martial arts skills, she might try something like female - only martial arts tournaments and face new rivals. Another could be her dealing with typical female - only social situations in school, like joining a girls - only club.