Ran, sister to Tenma Morimura, originates from modern-day Kyoto. Summoned into the parallel world of Kyou by the oni leader Akuram prior to Akane Motomiya's involvement, she failed to connect with the White Dragon (Ryuujin) to become the Priestess of the Dragon God. Consumed by despair and fear during the summoning, she instead reached out to the Black Dragon (Kokuryuu). This pact consumed her with the Black Dragon's power, erasing memories of her former existence and placing her under Akuram's sway.

Throughout the story, particularly in the manga, Ran grapples with the alter-ego forged by the Black Dragon's influence. Rescued by Akane and the Eight Guardians, she regained her lost memories of her original life but recalled nothing of her time controlled by the oni clan. Following her recovery, she remained within a protective barrier at a Kyou residence.

Leaving this sanctuary allowed the oni clan to detect her presence. Akuram attacked her and Akane, seizing three divine talismans from the Guardians and taking Ran captive once more. Her narrative centers on the conflict between her human identity and the supernatural forces manipulating her, with her bond to the Black Dragon fueling internal and external conflict across the series.