The Story of an Exploration Hero Who Has Worked His Way up From Common People 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

Takagi Kaito, a low status high schooler, your typical Mob character so to say, was just a normal everyday explorer who hunted slimes every day in the dungeons that appeared in Japan, earning pocket money while admiring his childhood friend, the class madonna, from afar. One day, a golden slime he had never seen appears before him. After he defeats it, he obtains an extremely rare item worth hundreds of millions as a drop, a servant card that can summon mythical beings!! After he makes up his mind and summons it, a warrior maiden with unparalleled beauty appears. Rise above being just a mob explorer Kaito! A modern battle fantasy story has begun!