im not sure but within my range of anime so far i say
saber of fate/stay night, with her scabbard cus then she's to be invincible wit the protection of avalon, though this pic tells somethiing diffrent
nanoha of magical girl...StrikerS, though hayate has a higher rank...maybe vivio's relic transformation mode too
...maybe the jigoku shoujo cus she can send anyone to hell and anytime