A Priestess and Her Guardian

[AU] Years ago, Soun, a forest spirit, gave up his powers to wed a human. But when his youngest daughter falls gravely ill, Soun returns to the forest and begs the current guardian, Genma, to save her. He agrees but on one condition: when Akane comes of age, she will serve as priestess to his heir, Ranma. [Ranma/Akane, some Akane/Ranko]