Asuka Tsuchimiya stands as the protagonist throughout the narrative. She begins as a cheerful, energetic high school student, enthusiastically active in her school's radio club alongside four friends. Her persistent curiosity fuels the group's regular performance of the "4:44 ritual" at their local shrine, involving prayer before a sacred tree while tuning a portable radio to random frequencies in search of alternate dimensions.

This ritual unexpectedly succeeds using a frequency discovered on a mysterious rock, hurling Asuka and her friends into a hostile parallel world. There, they meet Twilight Asuka, an alternate version distinguished by her serious demeanor and combat prowess. This counterpart reveals the existence of the Twilight, a cosmic force consuming entire universes and erasing their possibilities.

During subsequent interdimensional journeys, Asuka encounters multiple variants of herself across fragmented realities, each reflecting different personality traits or life circumstances. These encounters gradually unveil the multiversal threat's connection to her brother's disappearance, forging a deeply personal stake in the conflict.

Exposure to her alternate selves and escalating danger drives Asuka's significant development. Initially reliant on Twilight Asuka for protection against entities called Noizes, she eventually gains her own transformative capabilities. By the series' conclusion, she obtains an "Equalizer" device linked to her Walkman, unlocking combat abilities rivaling her Twilight counterpart, including flight, energy projection, forcefield generation, weapons creation, and dimensional travel.

The narrative culminates with Asuka confronting the ultimate manifestation of the Twilight threat and achieving a significant transformation. This final evolution grants her reality-warping capabilities, encompassing spatial and temporal manipulation, energy manipulation, matter manipulation, and universal-scale restoration powers. She ultimately reverses the Twilight's destruction, restoring consumed universes to their original states.

Her relationships with her four close friends—Yu Tounaka, Mia Silverstone, Nana Nanase, and Chloe Morisu—form a core aspect of her journey. Their shared experiences across dimensions involve confronting personal insecurities and parallel world versions of themselves, strengthening their bonds. These dynamics substantially contribute to Asuka's growth and her evolving approach to leadership within the group.