A Simple Task of Providing Support from the Shadows to Defeat the Demon Lord is a Manga/Manhwa/Manhua in english language, Adventure 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

Holy Brave, Toudou Naotsugu was summoned from another world to defeat the Demon Lord. Priest Ares was ordered to provide support for the the hero while hiding his true level, however... This is a story of High Priest Ares guiding the Holy Brave on their path to become a Hero.