In a flooded world, a boy rescues a robotic girl from the sea. Grateful, she vows to be his "leg" until fulfilling her former master's order, leading to an unforgettable summer adventure.

Spun off from The Idolm@ster (2011), this series follows a new group of idols working alongside the thirty-nine idols of the newly-formed 765PRO Live Theater base at 765 Productions and a producer at the 765 Theater Agency.