I'm the Only One Who Doesn't Know That Villainess Is Man

Vivian awakens to find herself possessing the body of a terminally-ill female lead, doomed to a tragic ending. Refusing to accept that fate, Vivian seeks out Rahel, the story’s infamous villainess and the only person capable of curing her. What begins as a desperate gamble slowly turns into a genuine bond, and against all expectations, the two become close, true friends. But...

"Not for a single moment did I ever consider you my friend, Vivian."
"Do you really think you could enter a contract marriage with anyone else?"

...Wait. Wasn’t Rahel supposed to be a villainess?! My best friend just turned out to be a guy?!