I Became A Childhood Friend of A Mid Level Boss 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

Do Kyunwoo is the black sheep of his renowned swordsman family. He cannot even catch a rabbit on his own. On his first day of fifth grade, he meets a tranfer student and recalls his past life. He had reincarnated into the world of a game he used to play called [Brave Hearts]. He was already frustrated that he had reincarnated as a loser, but on top of that, the transfer student is an intermediate/mid-tier boss who will destroy the world! “Why are you being so nice to me?” “Because I want to be friends with you.” Do Kyunwoo’s plan is to become friends with the transfer student in order to prevent the end of the world! In order to survive in this new world and to reach an ending he desires. He becomes best friends with the mid-tier boss.