They are Asami Sato and Korra, two of the main characters in the Nickelodeon series Avatar: The Legend of Korra. In the show itself, they are depicted as vying for the affections of a male character, Mako. Unfortunately, Mako is a douchenozzle, and because of this, and because of a few overanalyzed things in some episodes of the show, and because lesbians are awesome, a very large segment of the fanbase has begun to ship Korra and Asami with each other. The "Korrasami" ship is particularly common on tumblr, where it is the most popular ship. The line "OTP: Korrasami" is a reference to this; OTP means "One True Pairing".