A mysterious woman Ryuga encounters who retains memories of Kamen Rider Cross-Z. She was previously abandoned after surviving human experimentation in the former world. Her connection to the past and her safety become central motivations for Ryuga throughout the conflict.
Yui's past trauma is indirectly tied to the experiments conducted by Evolto's kind.
Ryuga takes on a protective role over Yui after meeting her in the new world.