Yui Kamishiro, one of the twin sisters alongside Mai Kamishiro, shares a bloodline connection to the ancient god Agama as relatives of Ken Taiga. This lineage grants them special abilities: telepathy, teleportation, and visions, enabling them to perceive distant events and receive prophetic insights, such as foreseeing Dragon Empire attacks or recognizing their long-lost brother Ryu Dolk by his dragon mark.

Their importance in the conflict against the Dragon Empire emerges when they present Ken with the Myojin Mirror, an artifact revealing Agama's historic battle against the evil god Drago and exposing the existence of Drago's sealing rock. They later pilot the mechanized Pegasus-like unit Begaruda, summoned to transport and support Ken in his Jushin Liger armor during battles against biomechanical beasts.

A pivotal development occurs through shared visions confirming Ryu Dolk, a Dragon Empire warrior, as their biological brother. This revelation complicates their loyalties as Ryu shifts from opposing Ken to allying with him, prompting the twins to intervene and reconcile Ryu with Ken's team. During a major assault on Tokyo, Yui and Mai locate and activate a hidden mechanism near a lake, summoning a defensive castle structure to counter Dragon Empire forces.

In the final battle against the revived Drago, their powers prove instrumental. Alongside Ken and Ryu, they fuse their consciousnesses with others to awaken Agama, channeling humanity's hope energy to defeat Drago in an otherworldly dimension. Surviving the conflict, they return to civilian life with other survivors. Their twelfth birthday coincides with the Dragon Empire's escalated efforts to revive Drago, intertwining their personal milestones with the overarching conflict.