AKB0048 Ep 6

This episode starts out with a promotional video of the 77th generation playing on the beach, while AKB48's latest single, at the time this anime was released, "Manatsu no Sounds Good" plays in the background.

Footage of idols playing around on the beach in swimsuits is not uncommon, and you will most often see idol photobooks that primarily consists of them in bikinis, no matter what their age.