Ryuusaku Murasame, nicknamed Ryu, is the eldest of the three Murasame brothers. A former kamikaze pilot who abandoned his mission during World War II, he later found the orphaned Tatsu by the roadside and adopted him, forging a strong familial bond with Kenji and Tatsu. This cemented Ryu's role as the group's caretaker, earning Kenji's deep devotion.

Memories of wartime rationing forged Ryu's intense aversion to food waste. He masterminded non-violent robberies in Tokyo alongside his brothers, targeting military blueprints and weapons of mass destruction with the goal of destroying them to eliminate such arms from the world.

Tatsu's death during Tetsujin 28's revival became a pivotal moment; Tatsu fell into the robot's rocket chamber and was crushed by its hand. Consumed by grief, Ryu placed Tatsu's body in a truck and deliberately rammed it into Tetsujin's leg, dying when the truck was partially crushed and ignited.

Earlier, Ryu instilled a lasting principle in Kenji: to rely solely on knives and reject guns. After Ryu's death, he appeared as a ghost, releasing Kenji from this vow by urging him to use guns against the PX Syndicate without guilt over their brothers' deaths.

The 2007 film adaptation diverges: Ryu survives the war and leads a small gang with Kenji. During the conflict, he briefly encountered Tsukie, learned of the Tetsujin project, and was shot by her. He maintained a friendship with "Shoutarou" from his kamikaze squadron days. Postwar, this "Shoutarou" and Shotaro sought Ryu's aid against Tsukie, culminating in him piloting a small plane while "Shoutarou" stood armed on the fuselage.

Manga portrayals offer alternate backgrounds: Ryu is depicted as either a criminal gang leader with Kenji as his assistant or a government agent. In both versions, he serves as Kenji's role model and advisor. His death during their mission leaves Kenji to complete their objective alone.