Watch Senran Kagura: Shinovi Master Online

Girls study at schools for modern shinobi. They dedicate their entire young lives to learning to become true shinobi, battling each other to polish their skills. And then one day, Asuka, whose grandfather is a legendary shinobi, encounters an ancient evil being named a "Youma" in the back alleys of Tokyo at Christmastime. Where there is light, there is shadow. Over 28 of the strongest and most well-endowed ninjas in history, both good and evil, will collide in a battle to determine true justice. And this deadly battle begins... right now. (Source: Crunchyroll)

At the renowned Hanzo Academy, a select group of students trains in secret to become ninjas of an elite clan known as the Shinobi Masters. Following her grandfather's footsteps, the hopeful Asuka undergoes this intensive training alongside her distinctive group of friends: Ikaruga, Katsuragi, Yagyuu, and Hibari. Relentlessly studying the secret ninja arts, they hone their skills in the hopes of one day becoming full-fledged female ninjas. Senran Kagura follows the girls as they fight valiantly against a mysterious new evil terrorizing Hanzo Academy. Dressed in tight clothing, they must prove their worth and protect the academy from its adversaries before it is too late! [Written by MAL Rewrite]

Special, unaired, episodes released with the Senran Kagura BD/DVDs.

A letter arrives at Death Cram School. Inside is a an invitation to a spa resort. Yumi declares to the four excited girls that, "No. This is evil itself," points out that they are slacking off too much. Shiki proposes, "When opinions are divided, it's time for boob rock-paper-scissors!" and then wins so they all go to the pool. There, girls from Hanzoo Academy, Homura Crimson Squad, and Hebijo Clandestine Girls' Academy also come, but Asuka says, "Let's have fun together today" and they call a temporary truce. However, a trivial matter sets off a sour quarrel and, at Yumi's suggestion, they settle it with a showdown in the style of the ancient shinobi. (Source: ANN)