DeepOne

Naoya and his twin sister Konoka lost their parents at a young age and endured a difficult childhood. Even so, they found happiness in life's small moments and wished their warm, peaceful days would last forever. That fragile hope is mercilessly crushed when a Grimoire suddenly appears before them. This forbidden magic book has existed since the beginning of time, yet it should not be in the human realm. Though they believed they were an ordinary family, they are actually heirs to the "Old One," a power capable of destabilizing the world.

DeepOne follows Naoya and his twin sister Konoka, whose hard-won peaceful life is destroyed by the arrival of a forbidden Grimoire. As heirs to the ancient Old One, the siblings are drawn into a supernatural conflict over a power capable of destabilizing the world.