My OP Skill is Single Use

It was the turn of the Millennium when the system first appeared in the world. The first dungeons came into existence, and the human race rose up to conquer them. Now society revolves around the gifts of the system; Levels and Skill Cards, cards that unlock superhuman abilities.

Connor had neither. A level one loser who had never unlocked a skill card, he could only watch as other people became heroes. So what is Connor to do when messages from an unknown number unlock a rare skill card for him? What is he to do when it's the most powerful skill he's ever even heard of? And how will he cope with the fact that unlike most people, he can only use his skill once?

Readers Can Expect: Comedy, Action, Numbers Going Up, A "normal guy" protagonist thrust into the world of dungeon delving and Hunter Politics with nothing but his wits and an OP skill he can't use.