Shirase Kobuchizawa, a high school student in Gunma Prefecture, has been working multiple part-time jobs to save up one million yen for a civilian expedition to Antarctica. Her mother, Takako, went missing during a research trip there three years ago, and Shirase is determined to find any trace of her. One day, after nearly losing her savings in a dropped envelope, she is helped by Mari Tamaki, a classmate who feels stuck in an ordinary life and longs for something extraordinary. Inspired by Shirase’s fierce resolve, Mari decides to join her.

Mari takes a job at a convenience store, where she meets Hinata Miyake, a sharp-witted and gregarious girl who dropped out of high school after being bullied. Hinata overhears their Antarctic plans and eagerly volunteers to come along. The three of them attempt to secure spots on a privately organized Antarctic mission led by captain Gin Todo and her deputy Kanae Maekawa, who were also friends with Shirase’s mother. Their direct approach fails, but they soon meet Yuzuki Shiraishi, a child actress whose mother has signed her up to serve as a teen reporter on the same expedition. Yuzuki has never had real friends and dreads the isolation she expects on the trip. Mari, Shirase, and Hinata convince her that they can all go together, and Yuzuki’s mother agrees to let the three join as her daughter’s companions.

The four girls undergo summer training camp, learn ropes from the seasoned crew, and navigate personal friction. Mari’s childhood friend Megumi, jealous of the new friendships, spreads rumors but ultimately confesses and reconciles with Mari. On the overseas journey, a scare over a misplaced passport in Singapore nearly derails everything, but the group pulls together. They board the Antarctic observation ship in Fremantle, Australia, and cross the Southern Ocean, enduring rough seas, homesickness, and moments of self-doubt.

Upon reaching Antarctica, Shirase confronts the reality of her mother’s disappearance. In a climactic visit to an inland base camp, she discovers her mother’s laptop and finally accepts that Takako is not coming back. Supported by the other three, she breaks down and begins to heal. Hinata, meanwhile, faces her own past: during a live broadcast, former classmates who bullied her attempt to cheaply apologize, and Shirase defends her on air. Yuzuki, for the first time, experiences genuine friendship rather than professional relationships. Mari, who began the journey without a clear goal, emerges with a deeper sense of purpose and independence.

The story follows their return journey, with each girl changed by the experience. Back home, Megumi, who has started her own adventure in the Arctic, sends Mari a photo from the other end of the world, mirroring the journey that brought them all closer. The narrative arc balances the physical obstacles of polar travel with the emotional growth of four very different teenagers learning to trust each other and themselves.