Winter Polaris

Summary pulled directly from Steam - Some text may only be applicable to Steam platform

Winter Polaris is the latest visual novel from the creators of Narcissu and Ame no Marginal -Rain Marginal-

This visual novel is comprised of two stories, "Winter Polaris" and "Sweeper Swimmer".

Present-day Tokyo.
One day, the news starts reporting of a mysterious "disease" that is sweeping the world. People who become afflicted are reported to "disappear into thin air". As civilization slowly succumbs to the disease and grinds to a halt, the protagonist decides to flee to the mountains in hopes of avoiding the disease.

Years later, after the whole world has seemingly disappeared, the protagonist finds himself alone. In search of potential survivors like himself, he returns the ruins of a city. There he meets a girl waiting for him. While strange in many ways, the most bizarre is how she declares that she is an immortal.

Just what did she want with him?

Sweeper Swimmer

Elena lives on a small rustic island in the sea, working as a courier by boat delivering cargo to nearby islands.
One day, after a storm, she heads off to make deliveries after a large storm passes overnight, she comes across a girl floating in the sea, luckily still just barely alive. Rescuing the girl from the water, the girl drops a mysterious glass object, one made with craftsmanship and technology beyond anything Elena recognized.

Where did this girl come from? And where did that glass come from?