The story follows Arata Kasuga, a seemingly ordinary boy whose cousin Hijiri is abducted by a mysterious phenomenon. To rescue her, Arata enrolls in the Royal Biblia Academy, a school for mages. There, he joins the Trinity Seven, a group of seven powerful female mages, and must uncover the secrets of the 'Eternal Trinity' to confront the formidable 'Crimson Lord' and save both Hijiri and the world.

As an anime film sequel to a popular series, 'Trinity Seven: Heaven's Library & Crimson Lord' was generally met with a mixed to positive reception from fans of the original manga and anime. Viewers appreciated the continued action, character interactions, and visual style, though some found the plot to be somewhat convoluted or derivative of existing tropes within the harem and fantasy genres.

• Fans enjoyed the return of their favorite characters and the continuation of the series' signature blend of magic and comedy.
• The action sequences and animation quality were generally praised.
• Some critics and viewers felt the plot became overly complex and relied heavily on established genre conventions.

Google audience: Audience reception on platforms like Google is not widely aggregated for this specific film, but general sentiment from fan communities highlights enjoyment of the action and character dynamics, with some expressing mild critiques about plot predictability.

The film is a sequel to the 2017 movie 'Trinity Seven: The Movie – Eternity Library & Alchemical Girl', continuing the narrative arc of Arata Kasuga and the Trinity Seven.