In the quiet secondhand bookstore Tsuki Books in Tokyo's Shibuya district, Taro Yamamoto has perfected the art of emotional numbness three years after his devastating breakup with Yuki. His days follow a careful routine designed to protect his wounded heart—until he discovers a mysterious leather-bound book wedged behind some poetry volumes. The Manual for Lost Hearts has no author, no publisher; just impossibly specific instructions for healing different types of heartbreak, written in elegant script that seems to shift between languages. When Taro accidentally follows one of its instructions during his evening run, he experiences his first moment of genuine peace in years. Word spreads quietly through Tokyo's network of broken hearts as people discover that Taro possesses an uncanny ability to find exactly the right passage for their specific pain. A divorced teacher learns to rebuild her identity through pottery. A widowed businessman discovers how to honor his deceased wife while opening his heart to new love. A rejected teenager finds her chosen family among friends who truly see her. Each person who reads from the manual unlocks new pages that weren't there before, as if the book grows with every heart it touches. But when Yuki calls one autumn evening—returned to Tokyo after her marriage failed—Taro must confront the manual's most challenging chapter: "For Hearts Afraid to Break Again." As he investigates the book's mysterious origins, discovering identical copies in bookstores worldwide, Taro faces an impossible choice between the safety of his carefully constructed numbness and the terrifying vulnerability required to love again. A story about the magic hidden in ordinary moments, the courage required for second chances, and the possibility that broken hearts create their own mysterious ways of finding healing—and each other.