The Kagami family has passed a sacred scroll down through their family for generations. This scrolls bestows upon the eldest son the power to merge with a powerful beast. It is said that the beast has brought the family prosperity for centuries. Unknown to the Kagami family, however, is that the scroll was looted from the onmyodo temple where Mao and the others once studied.
Soma inherits the powerful beast after his elder brother proves unable to keep the monster in check. The former police officer begins murdering people indiscriminantly including his own grandmother. Once he is dead Soma offers himself to the beast and Hakubi quickly sweeps in to mentor the boy and pit him against Mao. Despite this, Soma understands that Mao is a compassionate and caring person, as the doctor tried to help him remove the demonic creature from its bond with him. Soma wants nothing more than to master the beast and restore the family name to prominance even if that pits him against Mao.
(Source: furinkan.com)
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