Qin Lang, an unemployed young man plagued by bad luck, unexpectedly obtains an old ledger called the Gengzi Fortune Register and becomes a Keeper of Fortune, able to collect and record the misfortune of people in the mortal world. He encounters Lin Xiaoman, a girl born with extraordinary good fortune, and together they fight against Fortune Devourers who steal other people's luck. Amid a battle over the fortunes and misfortunes of an entire city, Qin Lang comes to understand that guarding fortune is not about stealing luck, but about repaying debts and protecting others as he records the gains and losses of the human world.