Ruri is a Jumi Knight sworn to protect Pearl, his Jumi Guardian. A lapis lazuli core embedded in his chest marks him as a Jumi, a race hunted for their jewels. Pearl's habit of wandering lost in thought frequently triggers tense searches, leaving Ruri frantic. He exhibits a brash, impatient, and quick-tempered nature, often distrusting outsiders due to relentless Jumi persecution and jewel hunters.

His abrasive personality emerges during investigations, like aggressively questioning townsfolk about Pearl's location. Yet, he fiercely prioritizes Pearl's safety above all else, driven by a past failure to protect an earlier guardian. This failure haunts him, intensifying his protective instincts. A critical encounter with Pandora's Box saw Florina, the Jumi Clarius leader, temporarily restore Pearl's memories and true identity as Lady Blackpearl. This revealed Ruri's prior desert meeting with Blackpearl, where she scolded him for his failure before jewel hunter Sandra shattered her core, transforming her into the amnesiac Pearl whom Ruri found and pledged to serve.

As jewel hunter attacks escalate, claiming Jumi lives like Rubens, Esmeralda, and Diana, Ruri grows increasingly bitter and desperate. His determination to stop Sandra and save the Jumi race pushes him to seek outside help, collaborating with another adventurer to track Florina. Their journey leads to the Bejeweled City, where Ruri confronts Sandra and the Lord of Jewels. In the final battle, the Lord of Jewels consumes Pearl's core, spurring Ruri to fight the entity. After the protagonist petrifies upon shedding a tear to revive the Jumi, Ruri persuades the restored Jumi to create a new Teardrop Crystal together, revitalizing the protagonist and securing his race's survival.

Following these events, Ruri continues accompanying the protagonist on further adventures, extending his commitment to safeguarding others beyond Pearl.