Aria the scarlet ammo

"Aria is a volatile girl who wields two pistols and two swords and holds the highest rank in assault studies at a high school for young mercenaries. This pint-sized prodigy swoops in to save her classmate Kinji from a high-speed chase, but he ends up saving her after he switches from a boring wimp into a total hot shot. ... Convinced Kiinji's an ace, Aria strong-arms him into being her partner"--Container.