MEGACROSSOVER:
There is a big, Japan wide youth martial arts tournament. All entries of the appropriate age groups are accepted, male or female. The only rules are ring out, no interference, no killing, and no permanently crippling or disfiguring attacks, with both sides getting disqualified by time-out, and up to 15 minute matches, or pin or knock out that lasts at least 20 seconds. Ages are from 11 to 19. There is large motivation to join, as the the prizes for the top 16 are all good, and the prize for #1 is huge, a mansion and a ton of yen (10 million or something big enough to motivate a lot of people), and round trip tickets to a location of your choice. Even the schools or dojos have motivation to get students attending who are talented in martial arts to join, as a high school or junior high with someone who gets into the top 16 gets similar monetary prizes, not to mention notable prestige, or if someone enters through a dojo, that dojo also gets a lesser prize compared to the school they attend, but still worth it for the dojo.
It is also an ultimate venue to prove oneself or defeat rivals, and isn't televised because they actually expect some weird special attacks, and the recruiters have admitted this. The entire thing is run by the Kyoto Magic Association and the Shinmei-ryu and paid for by them jointly with Hakubi Washuu and the Masaki clan. It was planned mostly by Washuu originally, after she remembered her purpose and found out about the high levels of spirit magic and ki powers found in some circles on earth, she doubts there will be anything that can rival a greater kami like herself or the other choushin, or even rival Tenchi, but she'd like to check and see in case there is something of intrest, especially as it is highly possible something of earth interacting with Tenchi's Jurai heritage created his abilities, and she knows Earth produced Seina.
The judges/referees are Eishun, Takahata, and Katsuhito. The commentators are Fuurinji Hayato and Konno "Kitsune" Mitsune (suggested by Aoyama Mokoto), and the great Hakubi Washuu herself.
The qualification test involves defeating special robots made by Washuu which have about the strength, speed, and toughness of a non-ki powered good normal human athelete, and about the skill of a 1st dan average black belt equivalent in a generic and versatile style created by the Galaxy Police for subduing criminals without causing permanent harm. What makes the robot special is that they have particularly exacting correct execution of techniques and powerful senses, and they have an above average ability to read an opponent that increases as the battle goes on due to the way Washuu programmed their AI's to read the opponent's style. It is a rather difficult qualifier for normal martial artists, but anyone with special ki powers or above 1st dan level in skill in their particular style has reasonable odds of defeating the robots. They are, for instance, below the level of Tendo Akane at the start of Ranma 1/2 manga in skill and strength, although similar in speed and toughness. The purpose of them is to filter out more of the normal martial artists and street fighters and such, but there is still many who can get past them.
Some of the star entrants include:
Saotome Ranma
Shirihama Kenichi
Aoyama Mokoto
Fuurinji Miu
Setsuna Sakurazaki
Kasugano Sakura
Natsume Atsuko "NukuNuku"
Kanzuki Karin
Hibiki Ryoga
Urameshi Yusuke
Kuwabara Kazuma
Gettou "Mikiri"
Takamachi Kyoya
Kakamachi Miyuki
Shidou Hikaru
Let the chaos begin, and may Washuu's data collection prove very interesting.
Edit addition: I'd like to see a situation where onna-Ranma, Fuurinji Miu, and Shidou Hikaru are all standing near each other, preferably in some sort of conversation, and someone else noticing and finding something eerie about the pigtails, or perhaps with Ranma standing in the middle and someone like Koalla Su looking between them and saying "It grows!" and noting their heights and breasts. Or at least just Shidou Hikaru and onna-Ranma and seeing them standing next to each other causing Ryoga to freak out and think Ranma has been cloned or something.
"Health, Learning & Virtue will ensure your happiness; they will give you a quiet conscience, private esteem & public honor." Thomas Jefferson (1743 - 1826)