Over on the Wild Mass Guessing page for Negima at TV Tropes, someone has suggested Haruna's is Ranma and Nabiki's daughter. Or Ranma and Akane's, but she's spent a lot of time with Aunt Nabiki.
-- Bob
---------
Then the horns kicked in...
...and my shoes began to squeak.
-- Bob
---------
Then the horns kicked in...
...and my shoes began to squeak.