Tsumugi Wenders, a 16-year-old half-German girl, ventures to Torishirojima Island during summer vacation to seek her life’s purpose. Standing 152 cm tall with a slender 38 kg frame, she sports blond twin tails with spiky bangs, green eyes, and a pale complexion. Her wardrobe favors a school uniform layered with a sleeveless sweater, knee-high socks, and loafers, often accented by a bell or hairpin. Honest and diligent, Tsumugi reveres tradition, adhering to rules and classical principles she views as time-tested rational guides, even when outdated. Though steadfast in her beliefs, she avoids imposing them on others, balancing strictness with gentle kindness. Challenges to her ideals provoke a flustered “mugyu,” while her occasional absentmindedness surfaces in vacant stares, monotone speech, or a disheveled appearance reminiscent of traversing wild landscapes. Her life intertwines with old foreign melodies she hums habitually, a collection of stuffed animals, and beachcombing—a pastime where she salvages sea debris for repurposing. Guided by introspection, she explores the island’s lighthouse, a site that draws her into a confrontation with a mysterious self dwelling beyond time, severed from reality by entanglement with the Tachibana of the Lost, a tree unbound by temporal laws. Friction arises when others question her rigid principles, yet she persists with optimism. Her journey culminates in the lighthouse, where encountering her original self triggers her fleeting disappearance. Reuniting with the protagonist later, she solidifies her resolve to embrace her identity. Expanded narratives reaffirm her growth, depicting her return to the real world as acceptance of her place within the timeline.