The idea is thus, after Galaxia, which ends a few months before the Saffron arc, the senshi discover that the crystal tokyo future they visited was only one possibilty of many, and that their future has already diverged, so both Chibi-Usa and Chibi-Chibi have to be sent back to where they came from in order to prevent Paradox. Sailor Pluto explians that Crystal Tokyo was not a very good future anyway because in it the Sailor Scouts were the ones who caused the great ice and the Black Moon Family actually wasn't entirely morally reprehensible as the Queen Serenity in that future had actually used the Ginsuzishou to 'purify' people and take away their free will so that the couldn't do evil, and had scewed the balance of law and order, good and evil, allowing for more powerful evils to form outside the Solar System and leave it under constant bombardment from evil and chaotic forces. Crystal Tokyo the Outer Senshi had been fighting to protect was actually simply a poetic reference to Tokyo as it allready was. Since the future has diverged, Sailor Pluto is no longer certain that the threats Chibi-Usa had brought back with her detailed from the future Pluto were ones that the Sailor Senshi would actually face, especially since Galaxia wasn't on that list and her forces were protected from Pluto's scrying magic.
Enter a new enemy, which first strikes soon after the failed wedding. Happosai, in a misguided attempt to control Ranma, releases a trapped
'demon' who contacts him spiritually to 'teach Ranma a lesson', this 'demon' is Jaidete of the Dark Generals, who has been trapped in his crystal prison for a long time after he failed to defeat the senshi, with his queen dead, metalia and most of the youma destroyed, Jaidete finds out about how strong the senshi have become, but thanks to Happosai, he finds a weapon against them, the high in life force residents of Nerima, with the multitude of martial artists and such not only provides plenty of life force for him to power and create youma and give him power to drain, but also provides him with powerful people to have youma possess and gain the skills and powers of, he takes over most of the NWC, and many other Nerima residents, Amazons, Musk, Phoenix People, Taro, etc. And creates a huge, very skilled and powerful army, which makes strategic strikes all over the world, forcing the Sailor Scouts to spread their forces. Jaidete honors his deal with Happosai in that he only beats Ranma up (although until Jaidete starts to take things seriously, Ranma gives him a pretty good fight). Jaidete also discovers an old magical control device created by Beyrl's scientists back during the Silver Millenium which was meant to counter the Ginsuzishou using Negaverse rather than moon celestial energy, and puts it to use for himself.
Ranma, driven by a need for revenge, and to free those made into slaves or batteries for Jaidete's army, and also needing a way to help maintain law and order in Tokyo, where some of Jaidete's forces were still attacking and kidnapping more people, and with the Sailor Scout split up fighting enemies more powerful than ever all over the world, they need support, goes to the Sailor Scouts to ask if there is a way to help, because he discovers that the demons drain his ki if he touches them or attacks them with ki blasts it only powers them up, and few of them are hot enough for the Hiryuu Shoten Ha, or weak enough for Ranma to affect much with shinto wards. Pluto, realizing how personal this was for Ranma, and Ranma's power potential, gives Ranma a Silver Millenium magical control device, designed by the last Queen Serenity herself, since Ranma has a powerful magical (linker) core (lesser version than a Sailor Star Seed found in mortals) and great potential as a mage, and teaches Ranma to use it, while using the power of the Time Gates to take all the scouts into them and train quickly (think Room of Spirit and Time in DBZ, training a year in a day type thing) in magic so that all the scouts, and Ranma, can actually defeat youma and free people of possession, rather than just Sailor Moon and herself.
Because this would be a fukufic, Ranma's 'strong armor' is a tux a la Tuxedo Mask in male form, and a basic serifuku in female form, which are pre-programmed into the device. Unfortunately, having magic doesn't mean control over or a cure of the curse, luckily, the inteligent device can swich Ranma's armor when Ranma gets splashed, leading to much hilarity.
A side note is that Jaidete isn't trying to kill civilians, he wants to take over the world if he can succeed at killing all the Sailor Scouts, turning everyone into possessed youmas under his command, but he _is_ trying to kill the Sailor Scouts.
I personally don't think I'm ready for a story this epic, but I'd love it if someone would take this idea and run with it.
