Hildegard is a character from the anime Blue Dragon: Trials of the Seven Shadows, where she is identified as one of the Investiture Beings. These beings are powerful entities who act as judges of the world's inhabitants, determining their worthiness to survive.

Hildegard possesses the unique and defining trait of having dual personalities, which correspond to both male and female identities. This duality makes her androgynous in her humanoid form, where she has long dark turquoise hair, green eyes, and pointed, elven ears. The distinction between the two personalities becomes most apparent in her true form, which is a long-necked dragon resembling a legendary lake creature. In this form, she has two heads, each one representing her male and female sides.

The female side of her personality is less serious and more playful. She tends to view her duties, including the trials she imposes on humans, as games, and seeks her own amusement in situations. This is demonstrated when she revives the shadow of a human opponent simply to make her game more interesting. In contrast, her male side is much more serious and controlled. While both personalities are present, the female side is often the more immediately apparent in her interactions.

Despite her dual nature, Hildegard is primarily characterized by her strict obedience to the rules of the high council of Investiture Beings. She follows executive orders without hesitation, showing little regard for the value of individual lives, whether human or even her own kin. She shows no remorse when tasked with punishing a fellow Investiture Being for treason. However, her dedication to these rules is absolute, and she will refuse orders that violate them. When the conflict among her kind escalates, she remains neutral, dismissing direct commands from her leader to uphold the established regulations.

In the story, Hildegard is a consistent obstacle for the protagonists. In her first major confrontation, she and another Investiture Being, Fagino, challenge the main characters to a game where the destruction of a city hinges on whether they can land a single touch. Hildegard and Fagino easily fend off all attacks and ultimately destroy the city. She later engages a human pilot in combat, and after toying with him, she awakens his shadow power to make the fight more entertaining. She also battles other shadow wielders and follows orders to attack a former ally judged as a traitor. Her role evolves near the climax; after her leader is defeated, she finally gains an understanding of the strength of the human heart and accepts the beliefs of her more sympathetic kin.

Her key relationships are primarily with the other Investiture Beings. She frequently teams up with Fagino, and the two combine their attacks in battle. She serves the council leader loyally until his orders conflict with their established rules. She is also charged with executing her compatriot, Rottarace, for treason, a duty she undertakes without hesitation despite being personally shocked by the betrayal. After the final conflict, she accepts the younger Investiture Being, Noi, as her new leader.

In combat, Hildegard possesses incredible speed and power. Her signature ability is elasticity, allowing her to elongate her limbs and necks to incredible lengths, strong enough to break through solid rock. Her dragon form can fire powerful green energy beams, discharge electrical sparks, and create protective barriers. In her true dragon form, her power is immense, and she can even change the color of the sky when she releases her full energy.