My challenge for other writers is a crossover between Ranma1/2 and Suikoden:Tierkreis.
The rules for it is for Ranma to be banished from his world into the Ravine of the Infinity(by either a rival or Happosai).
From the Ranma timeline it is preferable that he be sent any time after the Shishi hokudan? arc.
The beginning timeline for Suikoden should be after Diadora sends the Hero, Chrodechild, and Liu into the ravine, to give a chance for Ranma to meet the the hero as well as be pulled out of the Ravine by the elder Scribe(it is optional for Ranma to be nervous when meeting the elder because of his past experience with people like Cologne and Happosai).
You can use the fact that Ranma was Banished from his world to keep him from using the other gates of the Infinity since he cannot return the way he came.
It is optional for Ranma to be a Starbearer but not required( though you would have to decide which character he would replace in being a starbearer).
the pairing can be Ranma/Chrodechild to give Ranma another Rival in the form of Asad and using Icas as a gag with Him trying to constantly get Ranma to stay as a girl.

This is about all i can think to add to the challenge.