Heavens Library & Crimson Lord brings back Arata, Lilith and the rest of the Trinity Seven to face off against the greatest enemy in the history of the Trinity Seven; Lilith’s own father, who is revealed to be the strongest Demon Lord who challenges Arata who is now a Demon Lord candidate.

Arata inadvertently touches "Hermes Apocrypha," Lilith's Grimoire. Suddenly, he is enveloped by a bright white light, and a girl appears before him. She calls herself Lilim, and treats both Arata and Lilith as her parents. At the same time she appears, something changes in the world. The forbidden Eternal Library awakens.