First Stop Dungeon Rails, Book 1 - Michael Todd , Michael Anderle

Magic is a currency. Power is a debt. Freedom comes at a cost. Luke never planned on becoming a caretaker to a chaos fairy. Breaking the seal on an old puzzle box was supposed to be a simple job—appraise the relic, pocket the profit, and move on. Instead, he unleashes Riven, a mischievous, mana-hungry sprite bound to his life force.