The One Within the Villainess is a Manga/Manhwa/Manhua in english language, REINCARNATION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

In order to clear the name of 'Emi,' a girl who had reincarnated as Remilia, the villainess of an otome game, the real Remilia who had been watching all along inside awakens. Now it's time for the true villainess' revenge to begin!