The character known as the Great Witch appears in the anime Helck as a mysterious figure residing on a remote island where the protagonists become stranded. Her background is deliberately left ambiguous, though her appearance suggests a connection to the demon empire. She bears a striking physical resemblance to the demon Vermilio, appearing as an older version of her with a large witch's hat. This resemblance leads other characters to speculate that she may be a relative or potentially even a future version of Vermilio herself, though her true identity is never confirmed. She appears to have lived on the island for a considerable time, having put up a magical barrier around her mountain home to keep the local inhabitants from disturbing her.

The Great Witch possesses a complex and layered personality. She initially presents as reclusive and somewhat irritable, having isolated herself specifically to avoid being bothered by the islanders. Her encounter with the protagonists reveals a playful side, as she teases the small creature Piwi by tickling him after he calls her an old hag. Despite this lightheartedness, she carries a profound sense of gravity and mystery, speaking in riddles and offering warnings that hint at future events. She seems to possess deep wisdom and knowledge about the wider world, including the existence of other continents beyond what the demon empire's inhabitants knew.

The Great Witch's primary motivation revolves around guiding Vermilio and Helck toward their destination while subtly influencing the course of future events. She helps the pair because she understands their need to return to the continent, providing them with crucial navigation information, supplies, and a magical engine for their boat. However, her deeper intentions are more enigmatic; she intentionally sends Helck away so she can speak with Vermilio alone, suggesting she has a specific agenda concerning the relationship between the two protagonists.

Her role in the story serves as a pivotal turning point for the main characters. She functions as a mentor figure, particularly for Vermilio, offering cryptic but essential warnings about the future. Most significantly, she reveals that Helck contains a vortex of powerful negative emotions within him that could potentially consume him and bring about a great calamity. She advises Vermilio to remain close to Helck as a reliable ally while also staying cautious, implying that when the critical moment arrives, Vermilio may need to make a difficult choice. This warning reshapes Vermilio's understanding of Helck and introduces an element of tension and foreshadowing into their partnership.

Her key relationship is with Vermilio, to whom she seems particularly connected. The Great Witch treats Vermilio differently from Helck, singling her out for private counsel and addressing her concerns directly. She also shares a bond with Piwi, the small creature who knows her well enough to guide Helck and Vermilio up the mountain to her home. Her relationship with Helck is more distant but observant; she notes something about him quietly upon their first meeting and uses his absence to speak confidentially with Vermilio. She does not develop significantly over the course of her appearance, as she remains a static but impactful figure whose purpose is to impart knowledge and then recede from the narrative.

The Great Witch possesses notable magical abilities, including the power to erect and dispel barriers around her mountain home. Vermilio senses an intense amount of magical power emanating from her, confirming her status as a being of significant strength. She also demonstrates knowledge of magical technology, providing the protagonists with a magical engine for their vessel. Her abilities extend to mystical foresight, as she seems capable of perceiving hidden aspects of Helck's nature and predicting potential future outcomes. The true extent of her powers remains largely undisclosed, maintaining her air of mystery and leaving many questions about her capabilities unanswered.