I'm thinking of writing a Ranma fan fic that is set in the USA instead of Japan for the following reasons:
1. While usually considered a cheap dodge, having Ranma be in a new locale is an easy and quick way to limit complexity and character interaction for the duration of the fic. If he is in Nerima, or anywhere in Japan, how do I keep other cast members from interfering? The fic would deal with Ranma dealing with the situation alone. If still in Japan, why wouldn't he go to Cologne for assistance or trick Happosai into helping him? How would I prevent the other members like his fiancees from trying to help him/ or in the case of rivals trying to sabotage him or be used against him? By sending Ranma to another country like the USA, I can keep most of the rest of the cast out of the story and force Ranma to deal with things himself. This makes it easier to focus on Ranma. Of course this assumes that the story doesn't take too much time, if it does they would start showing up within about a month. He still would be able to call and ask for advice if need be, so he is not completely cut off from those resources, but they will be unable to help him quickly or interfere.
2. Ranma acts slightly different when not around the rest of the cast, hides less of himself. Just look at the storylines without other cast members like the one in which he helps the perverted kid in the hospital or on the hotspring island. Ranma's actions are somewhat dependent on who is around him. When Ranma first meets people he is fairly respectful and polite until they do something to insult him. He shows the same amount of respect to people as they do him. That is why he uses honorifics while speaking to Kasumi and is insultive to people like Happosai (though even with Happosai when not upset will use Ojiisan, basically grandfather).
3. The fic will have Zombies and Vampires. Having the undead and set in Japan doesn't work that well. Japan is not a place undead are likely to be. More than 99% of the population is cremated, cemeteries don't have mausoleums/graves instead a plot would be filled with many urns full of ashes, basements/subterranean living places are not very common, etc. The Japanese have many spirits/demons/gods but really don't have very many zombie/vampire myths. In Japan the first literature to mention vampires was in the 1930's . They do have some undead creatures but they don't fit the fic I'm thinking of. Example of a Japanese undead is Nuribotoke which is an animated corpse that has dangling eyeballs, oozing black skin, and an extremely bloated stomach. It likes to dance and pretend to be a messenger of Buddha giving false prophecies. I could use a Chinese myth like the Jiang Shi which are undead but I don't really think those types would work for the fic. BTW Jiang Shi are reanimated corpses that hop around, killing living creatures to absorb life essence from their victims they're created when a persons soul doesn't leave the body at death.
4. Part of the fic is to show how different from normal people Ranma is. With that in mind having it set in the USA allows further alienation. Japanese culture differs from US culture. Having it set in the USA allows for cultural misunderstanding for example Japanese nodding their head up and down does not necessarily mean YES, flicking middle finger up does not mean what it does in the USA, a guy in Japan would not hold a door for a girl that is not his because it is seen as asking for a favor in return, showing the soles of your feet to people is a very large insult in Japan, etc. In the USA your expected to maintain eye contact with people who are talking, in Japan they are unaccustomed to that and view it as being rude and aggressive. Ranma uses nonverbal communication i.e body language more than every other character in the manga combined, used hand gestures 355 times in the manga according to a 1996 issue of Shonen Sunday, so likely to be some misunderstandings.
5. Religious differentials will have some importance -Ranma will be using Shinto wards and purification rituals since that is what he is likely to know. Possibly may have someone try to change Ranma's religion. Ranma is likely Buddhist and Shinto (many Japanese are more than one religion and being both Shinto and Buddhist is common). His religion is polytheistic, not monotheistic like most of western civilization. Ranma is shown to go to both Shinto and Buddhist shrines and is seen praying several times in the manga. From a Christian view point particularly the type that fear witches he'd be considered one. He worships the Kami (gods and spirits not all of which are good there are kami of evil, destruction, death, etc.). Ranma belief is not based solely on faith. He has seen the power of the Kami, he has touched the Kami (Oni and the ugly divine horse are kami for example), he has seen the Buddhist river that divides the land of the dead and the land of the living, he has glimpsed Nirvana (Buddhist version of heaven when one of the ghosts went there), Ranma is nearly a kami himself (in Shinto people can, are -the emperor is a kami- and do become kami and he is more powerful than a great number of them - there are something like 8 million kami and many are even weaker than regular humans).
6. Part of it would be set in a rural area. Allows more options and less holding back. A city would constrain Ranma because of potential loss of life. If you haven't noticed in his biggest battles the collateral damage was entire mountains Herb (mountain go bye bye) and Saffron battle (mountain go bye bye, weather patterns changed, flooding, and water ways were rerouted Phoenix mountain gets water again after years without it).