Ranma's training journey goes as usual until Jusenkyo where he falls into the spring of drowned WOW succubus (same looks and techniques as the succubus in the game).
Now there's two ways how this can go, either he goes to Nerima first and there'll be some slapstick humour with the NWC's reaction to the curse before he gets summoned to Azeroth.
Or he gets summoned to Azeroth immediately after he falls into the spring.
The summoner is a warlock who tries to get his/her lvl 20 succubus pet. Well, he/she gets Ranma, definitely not your normal succubus.
There are two ways where this could go
1) The warlock defeats Ranma since she's not used to her new form yet and can't fight well in it. This defeat places a geas on Ranma preventing her from rebelling against her 'master'. Ranma still has his male form, though and he won't be affected in that form.
2) Ranma defeats the warlock who really didn't expect to be attacked in that way. So, no bond and Ranma is free. But as she is new to the world and doesn't know where to go the warlock proposes to help her if she does the same. So Ranma decides to accompany the warlock on his/her journey. An Ranma isn't locked in this version either.
Now, male or female warlock? I'd say female would be the best choice since that would give me the possibility to add some romance later on since even in succubus form Ranma won't have any interest in males, which doiesn't mean she won't use her seduction powers on enemies to get what she wants.
The trickiest thing is to choose a race and faction for the warlock. If there's romance I'd like to have someone that would come closest to Ranma's ideal of beauty, so human would be the best match, but other good choices imho would be Blood Elf, Night Elf. I know that Draenei and Night Elves don't have any warlocks, but why not make an exception?
Ranma's powers: Male Ranma will have his martial arts moves (if he's summoned after he's lived in Nerima for a while then he'd have his more devastating techniques available) and learning curve. He could probably learn a lot of new fighting techniques and the use of weapons on Azeroth. The succubus powers are only available in Ranma's succubus form, but added to the Anything Goes style will be even deadlier. Ranma could become one of the powerhouses in the world of Azeroth.
Ranma would make an excellent spie and could infiltrate some demon ruled places as well as fit in with the Alliance.
So, Horde or Alliance?
Alliance would be best for Ranma if he were able to hide his curse (but then there's the water magnet part). I don't think the alliance would trust him at all, and especially the Scarlet Crusade would be after him.
Horde would probably be more accepting and since I'm more of a Horde player I'd prefer that option anyway.