"The Girl in Twilight" is a 12-episode anime series that blends elements of science fiction, fantasy, and drama. The narrative centers on a group of high school girls who discover a mysterious phenomenon involving parallel worlds. The protagonist, Asuka Tsuchimiya, and her friends—Nana Nanase, Yuu Tounaka, and Chloe Morisu—are members of the "Twilight Apostles," a club that investigates urban legends and supernatural occurrences. During one of their club activities, they encounter a strange radio wave that transports them to alternate realities.

Each alternate world presents a distorted version of their own reality, often reflecting the inner struggles or desires of the characters. These parallel worlds are governed by unique rules and populated by alternate versions of themselves, known as "Otherselves." The girls must navigate these worlds, confront their Otherselves, and resolve the conflicts that arise. These encounters force them to grapple with their own identities, fears, and unresolved emotions.

Asuka, the de facto leader, is pragmatic and determined, often taking charge in critical situations. Nana is cheerful and optimistic, providing emotional support to the group. Yuu is reserved and analytical, offering logical solutions to the challenges they face. Chloe, the most enigmatic of the group, harbors a mysterious past that becomes increasingly relevant as the story progresses. Their interactions and growth are central to the narrative, as they learn to rely on each other and confront their personal dilemmas.

The overarching plot involves a mysterious entity known as the "Twilight," which seems to be the source of the parallel worlds. As the girls delve deeper into these realities, they uncover clues about the nature of the Twilight and its connection to their own world. The series explores themes of identity, self-acceptance, and the impact of choices, as the characters are repeatedly challenged to reconcile their differences and face the consequences of their actions.

The story builds toward a climactic confrontation with the Twilight, where the girls must make difficult decisions to protect their world and each other. The resolution ties together the personal arcs of the characters while leaving room for interpretation regarding the true nature of the Twilight and its implications for their reality. The series balances episodic adventures with an overarching narrative, creating a cohesive exploration of its central themes and characters.