Reijirou Araki, formerly known as the Hand Shaker Break, fought alongside his partner Yukine as Team Chain within the Ziggurat dimension, wielding the "Metal Body" ability to transmute his entire form into impervious metal. After leaving active battles, he and Yukine encountered and adopted an infant, Yukiya Araki, under unusual circumstances. Aware of Yukiya's unique status as an irregular Hand Shaker, the couple dedicated themselves to shielding him from the dangers of that existence. Reijirou strictly instructed Yukiya to avoid physical contact to prevent triggering unwanted battles.

Professionally, Reijirou works as a music engineer, nurturing Yukiya's own passion for DJing and house music. His personality blends a hot-headed nature with a fundamentally caring and kind core, driving his protective instincts. This fierce protectiveness surfaced when he discovered Yukiya had entered the Ziggurat and drawn other Hand Shakers' attention, leading to a direct confrontation demanding answers.

Maintaining ties to his past, Reijirou attended the wedding of former Hand Shakers Team Card (Riri and Masaru). While he later learned Yukiya's biological parents are Nagaoka and Mayumi (Team Cocoon), who conceived him within the Ziggurat using a divine wish, Reijirou remained Yukiya's adoptive father. Following Yukiya's use of a wish to resolve the central conflict, resulting in the permanent loss of all Hand Shaker powers, Reijirou's mission to protect his son from that world concluded.