From an inconspicuous bottom-level explorer to a successful road! High school student Kaito Takagi, whose ability is so low that he can be called a passerby character, is an ordinary explorer. Every day, he hunts slimes in the mazes that appear in Japan. While trying to earn pocket money, he also has a crush on his childhood playmate who is the goddess of the class. One day, a golden slime that he has never seen before appeared in front of him. After defeating it in confusion, Kaito actually got a Servant Card that can summon a mythical existence. This is a super rare item worth hundreds of millions!! When he made up his mind to summon, a Valkyrie who is so beautiful that it is beyond human imagination appeared── Transform from a passerby explorer to a big man! The beginning of a modern fantasy battle story!