Six months after the battle in Venezia, Minna, Gertrud, and Erica are stationed at Saint-Trond Base in Belgica, joined by Karlsland witch Heidemarie. Ursula, Erica's twin, delivers a 50mm cannon and Jet Striker Unit, with Gertrud chosen to test them—despite Erica's concerns from a previous mishap. Erica later tests a Twin Striker with Ursula, but her impatience causes failure, leading to harsh words that dishearten Ursula. When Minna and Gertrud are ambushed by splitting Neuroi, Gertrud tries using the 50mm cannon but is overwhelmed. Hearing Minna in danger, Erica takes the Jet Striker and cannon herself, struggling to control them until Ursula arrives to help. Together, the sisters save Minna and defeat the Neuroi.