Reborn As The Heavenly Martial Demon is a Manga/Manhwa/Manhua in (English/Raw) language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.ManhwaZ.com fastest updating comic site. The Summary is
Humanity lost the war. Businessmen who sold out their fellow compatriots, hunters who turned to the monsters, stepping on countless human corpses, all in order to earn profit. The otherworldly monsters that entered our world seized it bit by bit like a raging fire. That was until Zuo Chi arrived. Back then you were happily invading our world, so why are you crying now?