"The Daughter of Terra" by Kevin D. Hammel
Can Ranma, Akane, and their new friends in Juuban survive destinies millennia in the making? This continues the classic Ranma/SM crossover “Lines of Destiny” by Louis-Philippe Giroux.
Worth a read, especially if you wanted to see how the Ranma and Akane relationship develops.
This is an authorized continuation on the part of Giroux and suggested by the author of the other major continuation, Shareon.
lines_of_destiny is the preceding series.