Shizuku "Drop" Sakuma, the spirited youngest addition to a trio famed for backyard explorations, enters the group upon the protagonist’s return from a year-long absence. Sparking their adventure, he persuades a friend to acquire a drone to film a fireworks show—a decision that propels their journey. Behind his playful demeanor lies a complex past, marked by years in Iceland where he encountered a telephone booth beside a waterfall he dubbed "golden," an encounter that profoundly influenced his outlook on life and human bonds.

Drop often speaks of a "treasure," misleading friends into envisioning a tangible prize. The truth surfaces that this treasure embodies cherished bonds and shared moments, especially their camaraderie. Clues to his fragile health emerge through mentions of hospitalizations and his labeling of their quest as a "final adventure," quietly hinting at his impending demise. After recovering the lost drone, he departs, bequeathing a map etched on Coca-Cola bottles that steers the group toward Iceland.

Their Icelandic voyage unravels Drop’s history: a misdialed call from the protagonist once drew him toward the trio. The waterfall’s telephone booth bridges his past with their present, a preserved note within affirming his treasure as their fellowship. Even after death, his legacy lingers—friends adopting his hairstyle, a tribute to his lasting imprint.

Drop’s journey underscores fleeting youth and enduring legacy, his cheerful facade clashing with silent battles against mortality. Through covert motives and deliberate choices, he steers the narrative through friendship, self-realization, and embracing grief, cementing his role as the cornerstone of his friends’ transformation.