Triela has a sarcastic wit and prefers to wear masculine clothing. She serves as a sort of mentor/Mother to the other girls of the SWA and she retains the most realistic outlook on their situation.
Triela's preferred weapons are the SIG-Sauer P230 SL pistol (after losing her P230 to Pinocchio, she is given a 232-SL as a replacement) and the M1897 Trench Shotgun with bayonet attachment. She has also been shown using a selection of Heckler & Koch weaponry, including the H&K G3A3 battle rifle, the H&K P7M8 pistol, H&K UMP submachine gun and H&K MP7 PDW.

She was former victim of a Mafia child smuggling group based in Amsterdam, Triela was one among many who regularly suffered abuse in the form of drugs, torture, rape and mutilation for the making of "snuff" films. She was rescued by a pair of Europol detectives, one of whom was her future handler, Hilshire. After being mortally wounded in a gunfight, Hilshire's partner bravely used the last of her strength to perform CPR on Triela, enabling Hilshire to save the child's life.
During the assault on the nuclear plant, Triela is severely wounded but manages to hold off several soldiers allowing Rico and Henrietta to advance further into the plant. Hilshire comes to her aid after Rico informs him that Triela had been injured. The two are last seen having died in each other’s arms presumably after being overrun by enemy soldiers. Their bodies are later found by Marco.
(Source: Gunslinger Girl Wikia)