Star Wars: The Clone Wars: 3x16

Altar of Mortis

Before the Jedi can leave Mortis, the Son takes Ahsoka captive in an attempt to entice Anakin into joining him to use their combined strength to overpower his Father and Sister. To this end, the Son casts Ahsoka under the spell of the dark side. Meanwhile, the Father attempts to stave off a disastrous showdown between his children and maintain the Force’s increasingly precarious balance on the planet. Fearing that the Son may be unstoppable, the Daughter does the forbidden by taking Obi-Wan Kenobi to the Altar of Mortis, wherein is kept the Dagger of Mortis, a weapon capable of killing a Force-wielder. The Son steals the weapon, and attempts to use it against his Father to steal his power and end his rule, but the Daughter sacrifices herself, placing herself in front of the blade.