The 4th Grader Demon Lord is a Manga/Manhwa/Manhua in english language, Comedy 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

Shining black armor... A fluttering cape... and... a creaky school bag on his back!? The rumored beautiful female transfer student is a Demon King from another world!