Setsuna begins to research soot blight syndrome to understand the shocking statement Rinne makes. The endemic disease keeps the island isolated and toys with Rinne, Karen and Sara's fates. But Rinne's mother Kuon knows something unexpected.

"I don't have time to spare!" Sara yells hurriedly. She has a hypothesis as to why Setsuna came back in time and that he and she are destined to be together, but Rinne confronts him with a dark truth. Crimson flames lick the heavens, bringing an end to a bloody history.

Rinne and Setsuna thought they had left their pasts behind. Then, Rinne is a horrible memory she cannot ignore. Meanwhile, Setsuna is faced with a new revelation. The situation changes suddenly as Rinne, believing new information she just learned sets out into the stormy night and raging sea, and disappears.

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.