Knives Millions

Millions Knives (ミリオンズ・ナイヴズ|Mirionzu Naivuzu) is one of the few fully sentient Plants and the twin brother of Vash The Stampede. They are both born during a mission to further the human race, and they are taken care of by Rem Saverem until Knives disrupts the course of the ships, causing them to crash. While Vash believes all beings have potential for good and deserve life, Knives believes in the survival of the fittest. After discovering experiments performed on other plants, he decides that humans are evil and grotesque, and that they need to be eradicated. Vash does not agree with his plans and seeks to stop him, and Knives seeks to dissuade Vash from basing his life around the "idealistic nonsense" preached by Rem.
 * Adult Millions Knives anime voices: Tooru Furusawa (Japanese), Bo Williams (English)
 * Young Millions Knives anime voices: Masamichi Ota (Japanese), Joshua Seth (English)

Many years after landing, the two meet in the city of July, and the face off leaves Vash without his left arm and Knives in a very critical state. He slowly regenerates over a period of time, and forms the Gung-Ho-Guns to act for him. After he revives and learns that he is slowly dying by using his abilities, he begins absorbing other plants into himself, which causes his powers to grow exponentially. After fusing with thousands of plants, Knives launches his "Ark", a floating ship designed to leave humans without any resources. As he absorbs more and more plants, his Ark takes on the form of a sentient organism, capable of defending itself and, in some cases, even teleporting short distances. Vash and Knives eventually fight for a final time, and after the battle, Knives saves Vash from the exploding Ark, and eventually turns into a tree.

In the anime, Vash manages to locate Knives and the two have a massive battle. Vash manages to gain the upper hand and defeats Knives by disabling him. He then picks up Knives and heads back into the town he was currently staying at with Milly Thompson and Meryl Stryfe.