Millions Knives, known simply as Knives, is the main antagonist of the anime Trigun. He is one of the few fully sentient Plants and the older twin brother of Vash the Stampede. Knives and Vash were born on a human colony ship during a mission to settle a new world. They were raised by a human named Rem Saverem, who taught them compassion and respect for all life. However, Knives experienced verbal and physical abuse from a crew member named Steve, which planted seeds of resentment toward humanity. His outlook darkened further when he discovered that humans had performed cruel experiments on another sentient Plant named Tessla. Convinced that humans were parasitic and irredeemable, Knives manipulated the ship's crew into turning on each other and then redirected the entire fleet to crash onto the desert planet Gunsmoke, killing most of the colonists. Rem sacrificed herself to save the twins, but Knives reacted with satisfaction rather than grief.

After the crash, Knives and Vash survived on the planet. Knives hardened into a cold, calculating individual who believes in the survival of the fittest. He sees humans as a blight that must be wiped out to create a pure world for Plants. While he claims to act on logic, he harbors a possessive and obsessive love for Vash, viewing his brother as the only being worthy of standing beside him. Vash's commitment to peace and human life infuriates Knives, who dismisses it as foolish sentimentality inherited from Rem.

Knives serves as the driving force behind the series' conflict. He forms a group of assassins called the Gung-Ho Guns to hunt Vash and torment him. For most of the anime, Knives appears only in flashbacks, having been gravely wounded in an earlier battle with Vash that destroyed the city of July. During that confrontation, Vash lost his left arm and Knives was nearly killed, forced into a stasis tube to regenerate over decades. When he finally recovers, he confronts Vash one last time. Though evenly matched, Vash ultimately disables Knives with multiple gunshots and carries him away, intending to rehabilitate him.

Knives possesses all the abilities of a sentient Plant. He can generate and control powerful blasts of energy, often channeled through his right arm in a form known as an Angel Arm, capable of immense destruction. He has exceptional regenerative powers, allowing him to heal from fatal injuries over time. He can also psychically influence other Plants, bending them to his will. In addition to his supernatural powers, Knives is a skilled gunman, wielding a black revolver identical to Vash's silver one.

His relationships are defined by his ideology. He views Rem's lessons as a lie and rejects her completely. His relationship with Vash is the core of his character; he desperately wants Vash to join him but cannot accept his brother's choices. Legato Bluesummers and the Gung-Ho Guns serve him with fanatical devotion, but Knives holds no affection for them. He is entirely focused on his mission to eliminate humanity and reclaim the planet for his own kind.

Over the course of the story, Knives's character remains largely inflexible in his beliefs. The anime ends with the suggestion that he may eventually be changed by Vash's relentless compassion, but his development is left open. In the manga, his character is depicted with more nuance, occasionally showing grief for fallen Plants and a desire to end the conflict with Vash peacefully if possible. Despite his role as a villain, Knives is defined by his tragic past, his unwavering conviction, and his deep but twisted bond with his brother.