Ryusuke Shikishima flies the Toraika B-3 vehicle as a pilot in the Earth resistance force's Mechander Robo team. He is the son of Dr. Shikishima, the scientist who created Mechander Robo as Earth's last defense against the invading Doron Empire. His younger sister is Mika Shikishima, who later becomes a pilot herself.

Both Ryusuke and Mika endured the loss of their mother in a childhood car accident, forging a bond through this shared trauma. This event shapes Ryusuke into a protective older brother figure for Mika, who sees him as a responsible and intelligent role model. Within the team, Ryusuke often acts as a stabilizing mediator between the more volatile personalities of Jimmy Orion and Kojiro Hachijima, consistently applying a calm and reasoned approach to conflicts. His demeanor defines him as the introspective and level-headed "Blue Oni," contrasting directly with Jimmy Orion's passionate and impulsive "Red Oni" traits.

When Mika demonstrates her determination to join the team as a pilot despite initial resistance due to her age, Ryusuke's established relationship with her informs this development. Following Mechander Robo's severe damage in battle, the robot is rebuilt to incorporate four component ships, leading to Mika's formal integration as the fourth pilot during this phase.