The Demon King Arrives 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

In this world, there is a legend that has existed for many years: One day, the demon king will appear in the world, and under his command, there are seven terrifying demons that will unleash darkness and despair upon the world.