Megumi Amano is the sister of Amano Jyaku, a demon-human hybrid. Her origins differ between continuities: the anime identifies her as a beast-man race (Jūjin) member, while the manga depicts her as a human granted demonic powers. She accompanies her brother to the human world, joining the quest to find the prophesied Chōjin, the supreme being destined to unite the three realms.

In the manga, Megumi exhibits ruthlessly malicious and sociopathic behavior. She habitually entraps men sexually to falsely accuse them of rape or consume them in her monstrous form. She develops a fierce rivalry with Akemi Itō after Tatsuo Nagumo chooses Akemi over her, culminating in Megumi summoning the sea demon king in a deadly attempt on Akemi's life, driven by pettiness and vengeance.

The anime significantly alters her personality, portraying her as kind-hearted, empathetic, and noble. She immediately believes Nagumo is the Chōjin and actively protects him. Her role expands considerably, including a romantic relationship with Takeaki Kiryū, Nagumo's cousin, which tragically ends when she is forced to kill Kiryū battling Münchhausen II. A subplot involves Kohōki, a demon banished for a past affair with her, who dies rescuing her.

Both versions consistently characterize Megumi as highly sexualized and openly nymphomaniac. The manga uses this trait predatorily, while the anime employs it for comedic effect or to highlight boldness without malice. Her demonic heritage grants her enhanced strength and shapeshifting capabilities, though specifics vary. She fights alongside her brother against demonic forces targeting the Chōjin, serving as a protector for Nagumo and Akemi during the conflict surrounding the Overfiend's emergence.