Mob kara Hajimaru Tansaku Eiyuutan

Takagi Kaito is a high schooler with very low stats, practically just a random mob. He is a common explorer who spends every single day diving into a dungeon that appears in Japan to hunt slimes. One day, a never-before-seen golden slime appears before him. Despite his confusion, he managed to defeat it, and what appears before him is a legendary, extremely rare item called a servant card. As he steeled his resolve and used it to summon, a valkyrie with a beauty beyond this world appears.