Kono Ai wa, Itan.

Bereft of family and searching for a place in the world, a young girl named Yoshino stumbles upon an obscure, weathered tome in an antique bookstore. Her innocent curiosity takes a terrifying turn when she accidentally unleashes Belial, a powerful devil bound within the pages. Rather than wreaking immediate havoc, the otherworldly entity presents her with a fateful proposition. Belial offers to grant her one absolute wish, but the bargain comes with a steep and binding price: in exchange for this miraculous favor, Yoshino must forfeit her independence and live alongside the devil for the remainder of her natural life. Bound by this eerie contract, Yoshino finds her solitary existence irreversibly altered. She must now navigate the perilous dynamics of sharing her days—and her destiny—with a supernatural companion, trapped in an unorthodox partnership that blurs the lines between salvation and damnation until her very last breath.