Kouka, the violent hIE who calls herself Lacia's first sister. With her control over the antibody network, she is planning to carry out a horrifying act of terrorism. When Arato learns that her scheme is putting Kengo in danger, Arato sets out to rescue Kengo with Lacia's help.

Arato is given two weeks of suspension after the fight between Methode and Lacia leaves him with paying 4.5 million yen worth of damages they caused. In order to apologize to his father Kozo who offered to pay half of the damages, Arato takes Lacia, Yuka, and Ryo to Tsukuba where a large-scale hIE experiment is being conducted.