The series focuses on the adventures of Arata Kasuga, a high school student who is targeted by Lilith, a teacher at a mystical school and given three choices in an effort to help save the breakdown phenomenon of the world by evil forces and while attempting to solve the mystery of his beloved cousin and childhood friend, Hijiri who disappeared to a difference space.

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.