The "three-person four-legged relay" is a traditional competition at Shinkai Academy's sports festival. Taisei, Akane, and Ryota will be participating as representatives of their class. Cheered on by their friends, the three practice hard, but Taisei is distracted by the mysterious voice he heard in Hakodate and can't seem to concentrate. Meanwhile, the Black Shinkansen appears between Ueno and Ōmiya. ERDA finally succeeds in capturing the Black Shinkansen, but...