The Sekirei Ashikabi

Ranma is a young man who has faced many trials in his short life, many of which would have killed or maimed men far older and more experienced than him.
The Sekirei are a race of aliens whose ship crashed on the Earth thousands of years ago, and lay undisturbed until it was discovered by the founders of the Megacorp MBI.

Ranma's greatest ongoing trial started little more than a year ago when he was pushed into a magical spring at Jusenkyo that cursed him such that he would turn into a girl whenever he's splashed with cold water. This is the story of what happened after Ranma was captured by MBI and they discovered that their female side was in fact a Sekirei.