"Demon's Plan" is a manga series set in a world where individuals possess unique abilities known as "Demon's Plans," which grant them supernatural powers. The story centers on Eiji Hattori, a young man who seeks revenge after his sister is brutally murdered by a group of powerful individuals known as the Seven Demon Sages. These sages are notorious for their immense strength and influence, ruling over society with their abilities. Eiji, initially powerless, undergoes a transformation when he awakens his own Demon's Plan, gaining the ability to manipulate gravity. This newfound power propels him into a dangerous journey to confront the sages and uncover the truth behind his sister's death.

The narrative explores themes of vengeance, justice, and the moral complexities of power. Eiji's quest brings him into conflict with various factions, including other Demon's Plan users, each with their own motivations and abilities. Along the way, he forms alliances with individuals who share his goal of dismantling the sages' oppressive rule. Key characters include Maria, a skilled fighter with her own tragic past, and Raito, a mysterious figure who aids Eiji while harboring secrets of his own. The sages, each with distinct personalities and powers, serve as formidable antagonists, challenging Eiji both physically and morally.

The plot unfolds through a series of battles and strategic confrontations, highlighting the diverse range of Demon's Plans and their creative applications in combat. As Eiji progresses, he uncovers deeper layers of the sages' influence, revealing a conspiracy that extends beyond his personal vendetta. The story balances action with moments of introspection, delving into the characters' backstories and the societal impact of the sages' dominance. "Demon's Plan" presents a straightforward yet engaging narrative, driven by its exploration of power dynamics and the pursuit of justice in a world where strength often dictates morality.