Rebirth of the Genius Assassin

"This is your last chance and your only reincarnation. Choose wisely.", the old bearded weirdo said and waved his hand. Then like paper Luna was tossed from the judgment hall to the era of the ancients. - - - Luna had never believed in rebirth nor reincarnation, but on the day she died, that was all she wished for and her desperate wish came true. He hid his face beneath a mask, but his alluring grey eyes beckoned her and stirred her soul. She would find out all his secrets, she made a promise to herself. The deadly assassin of the 21st century, reborn and getting stronger day by day, what is her destiny to have her fate tied to the cursed demon lord?