Shingeki no Kyojin

Shingeki no Kyojin (also known as Attack on Titan) is a 2013 anime series by Production I.G based off of a manga by Hajime Isayama.

Episode 6
Many unnamed naked giants known as Titans are seen being slain during a rainstorm by Mikasa Ackerman.

Episode 25
Annie Leonhart briefly Skinny Dips as she is in her titan form and runs through a river while by chased by Eren Yeager who is also in his titan form nude and steps into the river as well.