The OVA arrives after 12 episodes built on the certainty that Keel and Aoi would never stop reaching for each other across a broken world. This is what happens when they finally do. It does not resolve the world's problems or pretend the war ends with siblings reunited, it just shows you the cost of that reunion, and what they become after paying it.

Tide-Line Blue: Kyoudai is a single adventure drama OVA, released only on DVD as the thirteenth episode of the Tide-Line Blue series. The world is still marked by the Hammer of Eden, a catastrophe that killed six billion people and left 90% of the land underwater. Gould and Keel team up with the New United Nations and with the crew of Freedom, the only space station still left, which is tied to their father. Together they set out to send a strong broadcast around the globe carrying a new map of the world, so that everyone can access it.