I'm guessing the amount of people here who've watched the other series, so I'll give a little backstory.
Two doomed priestesses who end up falling in love constantly, the doomed comes from the Orochi, evil with a capital E, and has 8 "heads", who all control interesting looking mecha. The doomed comes from that to seal the Orochi, one of the priestesses must kill each other.
The moon priestess, the popular yet mysterious Chikane, realizes this earlier than the main chara, Himeko, slightly bumbling, good-hearted...kinda like Usagi, in a way.
Anywho, the two try to summon the goddess Ame no Murakumo, who appears as a counter to the Orochi mecha.
Several failed attempts are made, but Chikane, as mentioned earlier, semi-gets her memory back...and tries to force Himeko to hate her by several disturbing methods, as she couldn't bear to kill the reincarnated Himeko again.
Himeko, abandoned, turns to the 8th orochi head, who is unwillingly fighting his duty, and is also in love with the blonde.
Anywho, the series ends up in a heartwrenching scene where the two girls confess their love, as Chikane lays dying, stabbed by himeko. At the very end, Chikane promises that she will reincarnate, and though their memories will be lost, tells Himeko never to forget her. Himeko swears, and at the very ending credits, an older Himeko finds someone who just happens to look like Chikane.
...but what if that girl happened to be Ranma?
I admit the reasoning is weak, and may lead to OC, but there are several factors that do coincide.
Chikane excels at anything she sets her mind to, and Ranma's only really concentrated on the martial arts. Two, Chikane refuses to voice her true feelings, also similar. Three, Chikane ignores anything that annoys her, and the soul of ice has been used before, 4th, definite jealousy issues, Chikane can't stand himeko going out with someone else, Ranma interceding on Ryoga and Akane's date, his dealing with the reversed Shampoo...fifth, let's not forget those stunning blue eyes.
Another reason I'm considering Ranma is that it would make an interesting backstory through flashbacks and appearances of now older Nerima characters, and how the different Ranma came to be trapped as she is.
(shrugs)
I know it's odd, I'm placing it here as a why to see if anyone can help me flesh this out a little better on the reasoning side.
If nothing else, I can just take Ranma out and leave the Kannazuki elements in, but for some reason, Ranma seems to like he/she could work.
A different possibility for the backstory is for Ranma to get splashed during the Saffron fight, lose hold of the Gekkaja, and forcefully awakens the priestess, including the powerful katana that comes with the job....when she wakes up, she's feeling rather strange emotions, as well as a strange detachement from any of the girls...as well as being a fair bit taller and having long blue hair. She won't take no for an answer, and as the Nerima cast keeps trying to keep her there, she gets more and more distraught, angry, and loses more of herself, as every dreaming moment is of _her_, someone she's never met, but already feels far closer to then Akane...which scares her, as she's not used to feeling so strongly for someone...ever.
In essence, the fight with Saffron drew the attention of the patron goddess of the priestesses, and to help Himeko with some visual clues, she changed Ranma into a more Chikane looking physique, similar to what (could have) been done in the past. Hey, phoenix...whatever the plural is, are, even if Saffy's not a god, related to the sun's energy.
As I noted earlier, I'm hoping someone else can offer another perspective.






