As New Year’s Eve draws closer, preparations for a holiday party are underway in Petersburg. In anticipation of the event, Eila Ilmatar Juutilainen of the 501st Joint Fighter Wing is determined to take Sanya V. Litvyak on a leisurely walk around the city. However, despite Eila's best intentions, she gets interrupted every time she gets a chance to ask Sanya out, ruining the moment and separating the girls. To make things worse, a Neuroi is approaching the base, threatening both the squadmates and the celebration in Petersburg. [Written by MAL Rewrite]

Although "Petersburg Daisenryaku" is officially designated episode 13, the story takes place in between the seventh and eighth episodes of Brave Witches. It was screened in theaters on May 13, 2017, before being released as the seventh Blu-ray and DVD volume of the series on August 25, 2017. The episode earned 2.6 million yen in domestic box office revenues.