In an apocalyptic Japan fractured by Mount Fuji's eruption, teenager Rui survives under quarantine, attending school online while craving human connection beyond his family. His sole meaningful bond forms digitally with Michiru in Shizuoka—a region doomed by the next eruption. Defying imminent destruction and societal barriers, Rui resolves to meet her, driven by protective urgency and emotional hunger from their virtual relationship. The narrative positions him actively bridging physical and temporal divides, suggesting their connection spans multiple realities.

Michiru exists under Shizuoka's annihilation threat, initially resigned yet forging vulnerability with Rui online. Her fatalism about the disaster contrasts with hints she might unlock understanding or alteration of their timeline. Her exchanges with Rui spark a shift from passivity toward catalyzing cross-dimensional connection. She functions as both Rui's quest focus and an emergent agent within parallel worlds.

Confined to digital communication by quarantine, Rui and Michiru's bond intensifies through shared isolation and apocalyptic dread. Rui's deepening feelings fuel his attempts to shatter time and space for her. Their "tangled history" implies ties extending beyond their reality into parallel existences. Romance merges with sci-fi as Rui strives to breach Michiru's dimension—mechanics abstract—culminating in a climactic race to meet before annihilation, their survival across timelines unresolved.

Within the compressed narrative, Rui evolves from isolated angst to determined action through his fixation on Michiru. Michiru progresses from resignation toward complexity, potentially involving salvation or transcendence. Their personalities surface through online dynamics—Rui’s persistent urgency contrasting Michiru’s initial passivity—though deeper motivations remain unexplored, prioritizing the parallel-worlds apocalypse premise.

Parallel worlds define the story's sci-fi core. Rui's dimensional-crossing attempts imply multiple selves or realities, with unexplained mechanics enabling their reunion quest. This multiverse framework interrogates fate, connection, and salvation against doom, leaving their outcomes across timelines ambiguous.