Rushuna in Grenadier: "I have no more smiles for you."
There's also the point in Episode 6 where Yajiro, annoyed at his stay at the Peach Blossom Tower being interrupted by cannon fire, runs up to the top of the tower, and then slices the next incoming shell clean in half.
Let's also not forget Rushuna's moment in Episode 6. More or less cornered against a semi-giant robot, less than six shots in her revolver, unable to move freely because her underwear's been shot off, having managed to just stalemate a few bullets from the robot's gun by shooting them out of the air. That's got awesome written all over it already, but the robot's pilot ups the ante by revealing that the three fingers on the gun hand covered up three extra barrels. Yikes! How does Rushuna get past the hail of lead? She fires one shot at the lead bullet in the cloud, knocking its fragments into the next...which knocks its fragments into the next and the next and so on, continuing into the barrel and blowing the arm clean off. Four times as many bullets...with one shot. Kirika might be a witch, Vash the Stampede may be a force of nature, but Rushuna's probably a f***ing goddess...well, sorta.
Then there's her entire fight during the last episode.
Heck, there's a couple in every single episode. Rushuna is a walking cloud of awesome, when she's not being her Crouching Moron, Hidden Badass self. I nominate her fight in episode 1, where she still looks like she's going to be the Genki Girl comic relief. She and Yatchan are half a mile away from the castle, and a mook takes a long rifle shot at them. She slaps Yatchan out of the way, and shoots the rifleman. From long rifle distance. With a .38 revolver. Behind her back. Then she walks into the castle. She uses her six shots. She's surrounded by men armed with rifles and submachine guns, plus the boss who has a gatling gun. At which point she shows what she can really do. Between her Improbable Aiming Skills, Gun Fu, and Unorthodox Reload technique (which uses her large breasts) she takes out an entire courtyard of armed men without getting a scratch. She wraps up by picking off the boss as he flees. From maybe half a mile away, she fires six shots. She shoots off the guy's gatling gun, his armor, and all of his clothing.