Riki-Oh Saiga possesses superhuman strength and accelerated healing, allowing him to resist bullets and recover rapidly from wounds. He retains five bullets in his chest as mementos from a Yakuza attack. Born with a hexagram-shaped scar on his right hand, identified as the source of his power, he was separated from his twin brother Nachi during childhood. Their mother was executed for poisoning infants, after which a caretaker smuggled the brothers out of prison. Riki was later adopted by the Saiga family. Nachi's repeated cry of "Are you ready yet?" during a childhood game haunted Riki after their separation. Nachi bears a swastika-shaped scar on his left hand; the significance of both scars remains unexplained.

Muscular with long flowing hair, Riki's defining features are the hexagram scar and the five bullet wounds. His personality blends violent tendencies and a solitary nature, earning him the moniker "Wolf." Despite his ferocity, he demonstrates underlying kindness, sympathy for others, and a strong belief in karma, directing his ruthlessness primarily at evildoers. Trained in Naike Kenpo, a martial art focused on qi gong that enhances his combat, his techniques include generating destructive air pressure with his punches and tearing human bodies apart effortlessly.

In sequel events, Riki arrives in the town of Misaki, dominated by illegal nuclear power plants and the religious-military group "God's Judgment." Captured and imprisoned, he is forced into gladiatorial matches within an arena. During his imprisonment, he discovers Nachi, who has gained the title "Savior" through his own psychic powers. Their reunion becomes strained due to Nachi's lingering resentment over their separation and abandonment. Riki engages in combat against numerous soldiers, displaying less restraint and more extreme violence than before.