Academy City's Daihasei Festival is approaching, and the festival's steering committee is charged with recruiting at least two Level 5s to take the athlete's pledge during the opening ceremonies. However, getting volunteers proves to be a challenge.

As the Daihasei Festival begins, Uiharu and Saten enjoy themselves, while Kuroko sees to her Judgment duties. Mikoto and Kongo run an eventful three-legged race against teams from other schools. A plot involving MEMBER begins going into motion.

The Tokiwadai team competes in the Balloon Hunter event, but due to a case of mistaken identity, one of the Sisters substitutes for Mikoto. Yoshio Baba feeds the other school's team with data on the Tokiwadai competitors, with surprising results.

Saten's quest for Shadow Metal ends up landing her in trouble. Uiharu notices something amiss with the website Saten was browsing. Mikoto learns that Wannai did not get her gym uniform returned, prompting her to go track down her Sister.

With her closest friends now giving her the cold shoulder, Mikoto feels isolated and helpless, but finds a surprise ally in Kongo. Kongo tries to track down any clues that will lead her to the whereabouts of Mikoto's missing "twin sister."

Saten carries an injured Kongo to safety, while Awatsuki and Wannai tackle Yoshio Baba and his robotic Great Danes. Mikoto spots Saten with Kongo in an ambulance, blames herself for getting Kongo hurt, and determines to set things right.