The original fourth dragon, which the ISDA name "Ostrum", wreaks havoc on Earth and then suddenly disappears before the ISDA can take action. Kasuga informs the ISDA that Ostrum has resonated with someone, but he does not know who. Ostrum later reappears, and enters into battle with the Lindworm Unit, but Ostrum overpowers them. Akira, who's watching from afar, decides to help her comrades, and joins in the battle with Machina. Meanwhile, Jin is helped by Kō, who takes him to Tartarus. Upon their arrival, Jin is obstructed by Kazuki, who still claims that Gio belongs to him. Back at the ISDA base, Kasuga is confronted by Yuuri. After refusing to answer her questions, he proceeds to have the computer drop the container holding the ISDA's original dragon sample. Ostrum, who had succeeded in losing the Lindworm Unit, appears in his Communicator form, and asks Kasuga why he decided to side with humans. Back on Tartarus, Gio is able to transform into his dragon form and flies off with Jin.

As Sieglinde and her comrades camp out in an abandoned building on an island, they stumble upon Sakaki, who has washed up on shore. Meanwhile, the ISDA conducts experiments on Laura, as Kazuki and Widow discuss her situation. At another location, Kasuga tells Yuuri about the purpose of the original dragons sent to Thanatos. Back on the island, Jin and the others question Sakaki about his motives. Gio later appears to attack Kasuga's location, but Jin's group comes to their rescue, though is incapable of dealing any sufficient damage. Just as Jin confronts Gio, Kazuki and Widow show up, but Widow is subsequently damaged by Gio after she attempts to blast Toa. As Thanatos is shown to be close at hand, Machina and Akira are shown to disappear from their ice tomb.