A young man named Reito Naoi, in his early twenties, is unjustly fired from his job. Consumed by a desire for revenge, he attempts to steal a valuable device from his former workplace, but the plan goes wrong and he ends up arrested. While in detention awaiting indictment, a lawyer makes him an unexpected offer: he will be released if he agrees to follow the instructions of the lawyer's client. With no other options, Reito accepts.

The client turns out to be Chifune Yanagisawa, the estranged half-sister of his late mother. When Reito admits he has no plans for the future, she gives him a single, peculiar order: to become the custodian of a great camphor tree standing on the grounds of Tsukigō Shrine. This tree is said to possess a mysterious power, and visitors come to it at night seeking something they have lost or wish to convey. Reito begins his new life as the keeper, living in a small residence on the shrine grounds and watching over the sacred tree.

In this role, he encounters a series of people, each carrying their own burdens. Among them are Yumi Saji, a university student who asks Reito to investigate why her father secretly visits the tree; her father Toshiaki Saji, a stern, middle-aged man who hums to the tree for hours; and Sōki Ōba, the reluctant heir to a traditional Japanese confectionery shop who comes to the tree with little faith in its power. As Reito spends his nights observing these visitors and listening to their stories, he begins to understand the quiet purpose of his new position. The tree seems to serve as a confidant for those facing their own mortality, allowing them to express words they cannot say to the living. Reito also presses his aunt, who remains a distant and enigmatic figure, for the full secret of the camphor tree, but she assures him that when he is ready for the answers, they will come to him on their own. Through his custodianship, the embittered young man gradually finds a new direction, learning how the act of guarding a place of solace can bring healing to others and, eventually, to himself.