King of the Octagon 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.nl fastest updating comic site. The Summary is

The thrilling MMA conquest of a rookie genius fighter Wheesung, who was a promising sportsman with a natural sense of movement, quit exercising in high school due to an injury and lives a part-time life. In the meantime, he is invited to the match of MMA amateur Junghwan … He feels a strong thrill at the power of ‘Octagon’ that he encounters for the first time. 22-year-old Hwi-sung Lee, who was busy running away after giving up on everything. The moment he climbs into the Octagon, a spectacular flight that no one expected begins.