Gai Kishiwada is a stargazing enthusiast who partners with his close friend Masataka Sakai as the Hand Shaker team "Rigel Pile," while Masataka operates as "Betelgeuse Pile." Fascinated by protagonist Yukiya Araki's unique ability to freely enter the alternate dimension Ziggurat, Gai is driven by the desire to obtain Yukiya's irregular Hand Shaker powers. His goal is to achieve a permanent life within Ziggurat alongside Masataka.

Gai and Masataka share a long-standing friendship rooted in their mutual passion for astronomy. Flashbacks show their childhood bond forged through shared stargazing, establishing a foundation of trust that extends into their Hand Shaker partnership. Their coordinated combat style incorporates celestial motifs, utilizing abilities like "Orion's Arrow" during battles in Ziggurat.

Initially positioned as antagonists, Gai and Masataka directly confront Yukiya and his allies to seize his powers. However, after being defeated in battle by Yukiya and Masarou Houjou, they reconsider their goals. This loss prompts them to abandon their pursuit of Yukiya's abilities and instead align with his group. They subsequently assist in opposing the primary antagonist, Midori Okuike.