When Kagari Shuuya wakes up in a white room, he's given a unique opportunity to reincarnate in another world with special powers. Opting to become a half-vampire with an affinity for Light magic, he unknowingly creates a new hybrid species known as Seivalt. Endowed with extraordinary abilities like Language Comprehension, Chain Projection, and Growth Modifier, Shuuya is thrust into a harsh underground realm where survival is grueling despite his advantages. Despite his prowess, the desolate landscape offers no solace or companionship, leading him to face a formidable white winged beast. In a brutal battle, Shuuya is nearly defeated, only to have his vampiric nature unleash a devastating power that transforms his foe. As the dust settles, Shuuya emerges as a small black cat, a Divine Beast reborn as a loyal companion for his future escapades.