In an underground shelter-city encased in ice, Setsuna meets a young girl named Rinne and begins helping her with a mysterious invention. It can apparently help save the world, but its true nature is unclear. Meanwhile, the city itself will very soon perish.

Setsuna rises up to create a future for a city without hope, but tragedy strikes time and again. Meanwhile, Rinne finishes her invention and Setsuna sets out for the future to save mankind's existence. Just before he goes, Setsuna makes a promise to Rinne.

Rinne and Rinne - A truth about these two girls is brought to light by a photograph, and Setsuna makes a decision. Will it make everyone happy? A new future awaits once this great mystery is solved. No more hesitating. It's the eternal finale.