The Genius Assassin Who Takes it All is a Manga/Manhwa/Manhua in english language, Action 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

I transmigrated into the novel I wrote. To change the ending that is destined for destruction, I must become the villain ‘Shin Kanghu’ and become stronger than the hero!