Ranma is somehow sent to the World of Full Metal Alchemist. Landing in Xing Ranma is arrested when it is believed that he tried to assassinate the Emporer. Ranma is given two options train to be the emporer's new Onmyōji or death.
The story takes place after Ranma has completed the training is completed with her taken the art of Alkahestry to untold levels. As the emporer's health depleets she decides that Ranma will sire him a new son ashured that passing on her strength will lead to Xings prosperity. With this fate in addition to the hoards of assassins from the various clans after her Ranma decides to escape.
The Special Alkahestry resembles Omyouji and coupled with his martial arts training makes Ranma a very dangerous person. Ranma has also learned how to use her ki and will as substitute for purification circles and necessary runes making it look similar to combat alchemy only he doesn't have to touch his palms together. also thanks to the dragon pulse he can transmit his energy anywhere he wants. Because of this his style would have to incorporate some circular properties maybe Xinyi Liuhe with cross-training in Baguazhang that coupled with his kenpo training might lead to something similar to the Takanayagi style from Tenjho Tenge.
Performing alkahestry with just his ki will require a great deal of energy maybe a technique where his reserves would continue to grow, but not to the rate where they would trash his body. At the same time he uses dampeners maybe tying of the flow inside his body so his body would only utilize the amount of energy he is trained to hold and use adequately. By dispelling the dampeners he gains abilities similar to those with a philosopher's stone but runs the risk of the upraise of ki easily obliterating him, or severely damage his body. Basically Ranma uses his ki to override the law of equivalent exchange and releasing the dampener's makes upgrades that ability to god like proportions proportional to the level of energy in his body similar to a philosopher's stone.