Nagasarete Airantō : ながされて藍蘭島 - "Nagaretsuite, Binzume" (流れついて、瓶詰) Episode 24

While Suzu was collecting seaweed by the coast, a bottle drifts ashore. Upon looking at it, she immediately presumed that it was the bottle that Ikuto had sent to his sister Misaki. She came back home to show it to Ikuto, and while reading the letter, it read that his sister went off to the sea to try to find Ikuto, but has gotten lost; therefore, Ikuto, Suzu and the other girls attempt different ways to get Ikuto out of the island to find Misaki.