Was Kakyoin Seduced by Dio?

Seduced by Dio, Kakyoin becomes one of the very first brainwashed Stand users.

Was Kakyoin supposed to be a girl?

It had something to do with araki wanting a female crusader, but the editor said it was a bad idea to have a girl as a main character in a shounen manga. So araki went with a softer male to foil jotaro instead. It didnt directly say kakyoin was going to be a girl, just that he replaced the idea of a girl.

How did Dio control Kakyoin?

First Meeting with Dio

Several months before the start of Stardust Crusaders, Kakyoin met Dio at Egypt. Dio sensed that Kakyoin was a Stand-wielder and challenged him to a duel. Kakyoin lost and Dio implanted a mind-control parasite on him.