Because of the mission, the scout army had to blend into Marley, here everyone saw the beach written in the book, armin and eren excitedly jumped into the sea, so did the others. Captain Levi didn't either. he can't hide his surprise, but he doesn't show it, he looks at the beach, musing cool breeze blowing and waves crashing, you happily run into the sea to pick up beautiful seashells, enjoy the blue beach Levi: "..."