With some of the AKB successors attending a peace ceremony, Kanata, Mimori, Chieri and 76th gen understudy Megumi are chosen to be stand-ins for the next concert. As Chieri's standing in for Yūko invokes jealousy from the 76th gen understudies, they dig up dirt on how her father is a manufacturer of DES weapons. Chieri explains to Nagisa about how she ran away from home when she heard her father's machines were being used by DES. As Kanata chases after Chieri, reminding her that her father should not affect her dream, Minami, Yūko and some other successors who believe Kanata should be made into a successor follow Tsubasa to where she meets Sensei-Sensei. There, they discover a cave full of Kirara, which shows a mirror of who succeeds the original AKB48 member, predicting Kanata will succeed Minami, who does not take it well.
襲名メンバーが劇場に出演できない場合に備え、
代役を研究生が務めるというアンダー制が導入されることになった。
77期生からはただひとり、智恵理が優子のアンダーに選ばれる。不満を持つ76期生。
今やすっかり優子推しとなった凪沙も複雑な感情を抱くが、
智恵理が優子のアンダーになりきろうと一生懸命なのを知り、
そんな気持ちは吹き飛んでしまう。
しかし、76期生が智恵理が隠し続けてきた秘密を暴き……。
