I like many people get story idea's fairly frequently but rarely do I make an attempt to write them. When I do make an attempt to do so I either do not like them, so they end up in the recycle bin, or I procrastinate until I no longer am interested in the idea. Here is an idea I've had but have no intention of writing. It is a Ranma ½/Dark Angel crossover.
Ranma ½ is extremely easy to crossover with other series, which is part of the reason it has such a high ratio of crossover fan fiction. Quite often I will watch a television show, read a manga, or watch a movie and decide to look for a Ranma fic that crosses over with it. A surprisingly large number of times I find it crossovered with what ever I happen to look for. For example, there is at least one Ranma ½/Dark Angel crossover in existence that I know about. I don't particularly like it but it exists. In that crossover Ranma is in a similar situation to Max (main character of Dark Angel) an escapee from Manticore just a different type.
Some background information about Dark Angel is probably helpful and can be gotten in a number of places like wikipedia (which is generally good for the basics but not so good with minute details and things open to interpretation). Here's the basics though: Dark Angel was a pretty good television show on Fox that ran for two seasons before it was canceled. The show was about a genetically engineered super soldier named Max. It was set in a near future United States that has gone to hell because an electromagnetic pulse did major damage (if a nuclear explosion occurred 200 miles up it's electromagnetic pulse could blow transformers all across the country as well as fry many electronics). Max, was created by the United States military as a super soldier via genetic engineering and escaped, the government of course wants her back.
The main reason I would like to cross these two series together is because both series use various means of eugenics. Dark Angel has the genetically engineered super soldiers, which Max is one of, and later we learn about a 4000 year old cult that has created super warriors via selective breeding. Though really the use of some type of eugenics is far more common than people think, both the USA and Japan had them in the past and they still exist in some form or other in many places of the world (though many of them are more benign such as genetic testing to determine if children will inherit/develop a genetic disease).
The Ranma manga has several eugenic programs.
The Joketsuzoku, Shampoo's people, have a law in which at least the girls marry strong males (whether it applies to the other gender is unknown and doesn't come up in the manga). This is a form of eugenics - mating the best physical specimens.
The Musk who seclude themselves until adulthood training like the Spartans and who used the magic of Jusenkyo, specifically using Nyannichuan, to mix animal DNA into their bloodlines to get the abilities of the animals (practice of using Jusenkyo to acquire animal abilities is no longer used by the time of the manga).
The Phoenix people used a magical spring of similar nature to Jusenkyo to acquire bird characteristics and use Jusendo to force the ascension of Saffron.
The last people we know of that might (no direct evidence) practice a type of eugenics is Ranma's family. Comments by Genma and that his ancestors are shown to be martial artists leads to the idea that it is likely that his family has been marrying martial arts families for a long time.
The basic idea would be to have an organization attempt to use Ranma, Max, and Shampoo for unethical exploration in the creation of better super soldiers. The antagonists would try to figure out what are acquired characteristics and what are because of genetic manipulation (via science, the magic of Jusenkyo, or selective breeding). They would attempt to use there scientific know how in combination with Jusenkyo to create super soldiers of unparalleled strength.
The choice of characters is because Ranma is the main character, chance to make up Ranma's lineage, and my favorite character. Shampoo because of the Amazons access to magic, their law (which is a form of selective breeding), and their antiquity. Max to tie the scientific and modern technological aspects of the story in. The Ranma storyline would likely diverge from the manga at sometime prior to the last volume, likely mid manga after Herb storyline, but at least mentions of the Phoenix people would show up in the story. Dark Angel would diverge from the storyline after the meeting of 4000 year old cult that used selective breeding (the cult and the amazon will have had numerous battles in their thousands of years of existence).
The story would start in Japan with one of the people from the cult attacking Shampoo. Ranma would get involved shortly thereafter. Shampoo would tell about the ongoing feud between her people and the ancient cult. Things would happen resulting in Ranma and Shampoo having to leave Japan for a while and ending up in Hong Kong. Things would happen in Hong Kong that leads Ranma and Shampoo to Seattle where they encounter Max.
Think it would be interesting to view some of the martial arts abilities as acquired characteristics that anyone with proper training could do but for some others to be solely because of genetics. This is a basic cast gets kidnapped and experimented on by unethical people, escape, and learn more about themselves and fight back against the people type fic.
That's all I have for this idea.