Zazie the Beast is actually a legion of insects that were the original inhabitants of planet Gunsmoke. The first other being they ever saw was Knives, who interested them greatly. It is unknown how they became members of the Gung Ho Guns, but from what they said through their hosts, they at first had hoped to live harmoniously with humans and plants, but they eventually decided they'd be more inclined to living with plants likes Knives.
Major Story Arcs
Knives Reborn and The Gathering
Zazie is seen at the resurfacing of Knives; he along with Leonof, Legato, Rai-Dei, Gray the Ninelives, Midvalley and Hoppered where there when Knives made Vash shoot with his Angel Arm into the moon, this lead to the formation of a huge crater on it. Two years later he is seen along with the Gung Ho Guns having a discussion on the true objective of the Gung Ho Guns: to make Vash suffer and to destroy his image of humanity. He is later seen observing a fight between Vash and Wolfwood, after Wolfwood killed Rai-Dei, who was trying to kill Vash, after losing to him.
Bottom of the Dark
After that, Zazie used one of his insects to spy on Vash's friends Milly and Meryl, who stopped a bad guy from harassing a girl in the town that they'd brought Vash and Wolfwood to for medical attention. He met with Midvalley and Hoppered after he kidnapped Meryl, to use her as bait. He then went to Vash and Wolfwood to give them the news. While the others were battling, Zazie decided to tell Meryl about Vash and Knives and how they were not actually humans but plants. Zazie was trying to see who was the winner of the two battles, but he is ultimately killed by Midvalley and Hoppered. Zazie is seen later inhabiting a new body, a young girl's body, and also manages to shoot Wolfwood and Hoppered. He is later seen after the intervention of Elendira, at the hospital treating his new human body.
Cross X and Zero Hour
Zazie has a little discussion with Wolfwood in the town that he and Vash were resting. He is later seen on Knives' Ark, were "they" (the legion of insects known as Zazie) have a little discussion with Elendira, where they tell him that Wolfwood and Chapel are dead, and that Livio and Razlo have joined Vash in his quest. They also say that they want to live in peace with either humans or plants. Zazie then takes down Elendira, and tries to take over Knives' body using a worm, but she is stopped by Legato, and Zazie's body is destroyed moments later by Knives. Still, the colony of insects uses another body to give Vash Zazie's Gung Ho Gun coin that he needed.
Powers & Abilities
Zazie is actually a colony of insects and worms that use a host as a means to continue their lives. They thought they could live along with plants and humans, but later they try to take over the plant population, but are defeated by Legato and Knives. They can paralyze their opponents, inhabit other people's bodies, and the bodies they inhabited typically had very good marksmanship. Zazie has also claimed that he/they can naturally feel the emotions of other living things.
In the anime Zazie is actually a troubled boy known as Bete, and though he looks like a normal boy, he is as deadly as any member of the Gung Ho Guns. His main weapons are .45 revolvers that he uses with very high precision. Zazie also has a high-frequency sound emitter in his ear, which he uses to control the giant worms in the desert surrounding the area. After Vash destroys that sound emitter, Zazie reveals himself and then proudly admits to being who he truly is, a Gung Ho Gun, and he expresses his hatred for the children that he had hidden among and that Vash had been protecting. He attempts to kill Vash with his gun, but Vash manages to dodge the shot and tries to talk some sense into him but is given no chance, as Zazie is killed seconds later by Wolfwood.