Vermeil in Gold - A Magician Pushes Through the Magical World With the Strongest Disaster 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

A student at the magic school, Alto, who was on the verge of repeating the school year, accidentally found a book that activated a magic circle, and as a result, summoned the sealed devil Vermeil! Vermeil is a very unhealthy older sister with a power devastating enough to be called a disaster! The apprentice magician walks side by side with the strongest being in existence!!